Since you referenced the Burris XTR 4-20x50 and the Bushnell 6-24x50, I'm going to suggest the Sightron SIII 6-24x50 as another option for you... The are available in FFP and SFP both. I went with the FFP version myself as I wanted to keep my subtensions the same no matter what magnification I am on. I have not found the floating center dot to be too large for "fine" work. The advantage of the SFP scope will be you'll most likely have more MOA or MIL available on your turrets... (FFP= 80 MOA SFP= 100 MOA) additionally you can dial your magnification down which will increase your subtensions which in turn gives you more room to shoot longer distances. The Sightron is Japanese glass and is on par with the Nightforce NXS as far as clarity. It does lack some of the features of the NXS (such as zero stop) but at half the price it's tough to beat.

AS far as MIL vs MOA get the reticle that you are familiar with using... I've always used MOA so I stayed with it. Do NOT get a scope that is both MIL and MOA (reticle and turrets need to be the same).

Lastly, the Primary Arms has had fantastic reviews and I've seen some demos It is a great place to "Start" if you don't want to break open the piggy bank just yet.