First Focal Plane(FFP) vs Second Focal Plane(SFP) for varmints

Am considering replacing my Sightron SIII 3.5-10x44 (excellent scope) for one with more magnification. The main use of my modified FP-XR in .223 will be varmint hunting and some (little) target work. Based on your experience, please give me some pros and cons of using SFP vs SFP for that intended purpose. I would assume an illuminated reticle would not be necessary or helpful. Price is a consideration but not the most important.

The Vortex and Leupold lines are currently highest on my lightly researched list.

The ffp scope "math" is easier as holdover mils are mils & holdover MOA is MOA @ any power. Ranging is the same.
The sfp scope is calibrated in Mils or Moa either @ max magnification/power(24x or @ max power and half power(24x and again @ 12x) depending on Manufacturer.
Due to this the "math" takes a little more awareness when you change from half power to full or vice versa.

FFP is usually more expensive to buy and enlarges the target AND the reticle when one zooms. So not a bad deal for tactical use @ close ranges and low power.
The SFP is good @ longer ranges if one considers that the reticle doesn't get bigger with power and possibly clutter the view. I personally like the fact that one can change the relative size of the Mils or MOA @ different power settings.

It is easy to learn either FFP or SFP, it just depends on what you get comfortable with.

In researching my recent purchase of a SIII 6-24x50 with MOA-2 reticle, I had the same questions. The only advantage I could see with the FFP is was were you needed the ability to quickly range, aquire and shoot various targets from close to far without the aid of a rangefinder. The Mil or MOA substensions stay the same at any power setting making the hold overs you had memorized straight forward, expecially in a timed match. Because I usually have a digital range finder and dope chart available when varmint hunting, I really don't want to spend a lot of time looking through a scope trying to estimate ranges. I can till still do so if need with the SFP at 24X (2-MOA) or 12X (4-MOA) if mirage is getting bad. And if I miss a Pdog, I adjust over to the dot/hash-mark where the bullet hit and shoot again. Most bench shooters also claimed they prefered the SPF over the FFP because the reticle did not grow as you increased power to cover the center ring at long distances. Once I determined I really did not need a FFP scope and some of the extra features offered on the Vortex PST, I went with the SIII which cost less than the Vortex PST.

Here is my reason why I am going to a FFP after every scope thus far being SFP.

1) Where I live, the vegetation reaches 4-5ft in height by mid summer unless mowed or actively grazed. Thus a lot higher than a coyotes back
2) Because it can be tough to predict where the dogs come from, it could be from 70 yards behind or to the side of me, or 250-350 yards away across open ground. So I tend to keep my magnification down near minimum until I actually spot one, then get on him and start dialing up the magnification (as long as they are coming in).
3) I have found it impractical to dial up to max magnification because of reduced situational awareness (I am hunting on a farm with livestock from sheep to horses, not to mention people, machinery, barns and the house). Max magnification also makes tracking the animal more difficult if they take off, and potentially impossible to lead if running. So I am almost always at some intermediate magnification.
4) My reticles so far have been the "plex" type (modified German #4), so while one can use the ends of the outer bars as reference points, the angle they subtend is all over the place since it changes by magnification. To know the magnification, you have to change your eye position quite a bit, not something I want to do while trying to take a shot.
5)If the range to the animal is changing, one may wish to hold over instead of dialing the scope (particularly if you don't have a custom elevation turret). But the reticle in a SFP scope is not too useful for hold over in a fluid situation. One ends up leading or holding high based on the depth of the critters body, this is not a very precise method when under stress. Coyotes are virtually always on a trot and go to warp 5 if spooked. Unlike out west, our eastern critters very often will not stop to look at you when provoked. So far, not one has come in to any form of electronic call. But they do run the other way pretty good.
6) if you regularly shoot at longer ranges, you may have a 250 yard zero. But beware, if shooting something like a 223 with 75gr match ammo, it could shoot up to 3" high at 100 yards and on a coyote that can easily be a miss. (I know, because I missed twice). So with a FFP, if I know that I need to hold 3MOA low at 100 yds, it is relatively easy to visualize with that reticle at intermediate magnification. Whereas the reticle is not much use to me at all at an indeterminate magnification with a SFP scope.

I have been working at this game for a year now and 1 wounding shot at 250 yards, a miss at 350 because my kentucky windage was off and 2 misses at 130 yards because the trajectory of the 75gr load and 250 yard zero had me shooting over the animals back. Given the number of opportunities I had and how many hours went into making that happen, as well as realizing how fast the action always goes down, I am now prepared to spend more money for a scope that provides me with reference points that are constant throughout its working range. I am familiar with the location, and no longer need a rangefinder for most spots I will shoot from and I print small drop charts on stickers that are visible from behind the gun.

So i think your needs will depend on the kind of terrain and cover you have in your situation, how the animal usually behaves, how much you can either anticipate or pick your shot and the degree of pressure you are going to be under to make a 1 shot kill. For me, 1 shot on the property and you are done with coyotes for the day. I only had 3 sightings in more than 6 months of hard hunting, but still took 2 animals, but it could have been 4. The farmer last year lost 80% of his lambs and 20% of his adult sheep before I arrived. Since then he has lost 1 adult sheep.

Thank you skypilot, jpdown, and Westcliffe01 for providing me the benefits of your experience. Your precise, detailed and articulate responses are most satisfying.

In my neck of the woods the woodchuck population is quickly diminishing and the coyote population quickly increasing. The benefit of your experience has me leaning heavily toward one more Sightron SIII or Vortex Viper HS w/SFP to continue long range woodchuck hunting. However, I can clearly see a Vortex, Bushnell, Leupold, etc. with FFP in the not-to-distant future as I slowly evolve into coyote hunting.

Best wishes,
John_M