Here are my thoughts on only the three options you listed.

1) So i honestly don't know anything about this cartridge, but here is practical info. First the cases. Despite what ANY online God tells you, this is 100% marketing business. Someone who begins to tell you something about how consistent Lapua is, immediately had no big data, and goes to strength. But again has no data to back it up. Well, we do have a Pressure Trace, and data. Lapua officially specs brass to 130% of that cartridges SAAMI/CIP MAP. Hornady as an example, specs to 125%. So if someone with a slogan to justify, tells you to "buy once, cry once"; make sure they know what they are talking about. Within SAAMI MAP, there is no practical life difference. Within the SAME amount of over pressure, there is no difference.
Moving on, this option is cheaper for bullets than your 308, and I would suspect less powder.
Are you sure this is the expensive route?

2) Several years ago part of my group of friends got into the distance with 223's game. We had fun and it is certainly possible. But beyond 1k the wind is a significant issue. If you live in windy country, this isn't a great idea. It if you really don't shoot that far that often, who cares.

3) My 308 that I shoot to a mile with, is starting to open up a tad, but she's well beyond 5,000 rounds; and want treated nice in the first half of its life. 308 bullets will be the most expensive of the cartridges listed.
Now the magical FlatLine bullets:
I did but them there moment they came out, and we did a bunch of pressure trace work with them. When they were first released, we(the public) were told that they can be pushed faster with less pressure. That in fact is a flat lie, a 150gr prohunter has A MUCH larger bearing surface area. Yet with the same case, load, and equal jump to lands, the pressures are statistically identical. Next we were told to not use slower powders like CFE. Yet again categorically false. We were told that the alloy used won't play well with regular fouling, again.... I think you get the idea.

So what is true about them? It is true that they absolutely will not cross trans-sonic safely. It is true that they have a stellar BC number.
If you believe in science and facts, then they can't be shot at higher velocities without higher pressures. Meaning that the whole notion about using "standard twists" is in question.
I'm not saying you shouldn't try them, or that they won't shoot well for you. I'm saying when any companies marketing department gets to run wild, and starts spewing garbage like "Just the tip, I promise". That company's claims sound be taken as seriously as the promise about just the tip......