On a hard kicker...I always want more eye relief. Had a 375 with an old Swaro way back....IIRC, it had about 3" of eye relief. Gun weighed about 10lbs or a bit more, but it still came back enough so every now and then, it would just kiss me above the eye. Not too hard, just enough to say hello and make me nervous.
I got rid of it. A 300 of the same weight would be more manageable, but if you are running a light setup...might not be so good.
Everyone is differently built too, and stock design and fit come into play....my rifles did not fit so well back then (another story) so I tended to crane my head forward alot to get my cheek down to the flat comb...causing my eyebrow/forehead to jut closer to the stock than other people might when my eye was lined up.
All that is to say...YMMV, but my experience wanted more than 3" on something that comes back a fair amount.
On FFP vs SFP...I prefer SFP, but then I grew up with it and also with old FFP reticles that got entirely too large for precise shooting at distance, at least the ones I was exposed to 20 years or so ago. Current designs, I believe, do not have this problem, the reticles are very fine at low power, so at top power they are not giant...that is they cover .1 MOA or whatever all the way through the focal range. Depending on the situation, there are some downsides to that, but everyone's needs and techniques are different. But I still prefer SFP because I do not use the reticle to range and I dial, don't like holding over. If I am shooting far enough to worry about wind, I am at max on my scope, so the windage marks will work on my VX6. My HD5, I have the lock turrets, so I just dial for wind. On my HST, I just dial. On the VX3i on my son's rifle, he has windplex, so he can dial for elevation and hold for wind.
Downside to this is holding over is definitely faster. But it's just not for me. I do have rifles where this is my only choice as they are not very repeatable, but I don't like it and am changing those scopes out for ones that I can dial reliably. But everyone is different. My probably most useful, and obvious, advice would be to make sure you go and look at the ones you are interested if you possibly can. That would probably give you your answer. You can see how they feel weight wise, see how close they are to your eye and get an idea of whether you think that will work, look at the reticles and see how they look at various zoom positions...etc. And perhaps most of all...see how they look...brightness, clarity, FOV, low light sharpness etc....
From what I have been reading (and it's all hearsay at this point) the new Vipers are supposed to be pretty great. Other than weight, they might be just what you are looking for. But hard to say just yet. Hope that helps!
