Re: Vortex viper 4-16x or 6-24x
FFP for sure.
Size difference in scopes is insignificant. Both have a 50mm objective. The 4-16 is 13.7" & 22.4 oz. The 6-24 is 15.5" & 23.4 oz. So no real difference.
Even at 400 yds. 6x magnification would typically not be too much. At 600 yds. would you want more than 16x? Below 150 yds. less than even 4x is sometimes too much, especially if in a heavily wooded area.
If it were me & most of my hunting was beyond 400 yds., I would probably go for a 6-24. If most of my hunting were between 150 yds. 600 yds. then I would prefer a 4-16. For 200 yds. and less I use a 1-6 or 2-7.
BTW, I have a 6-24 Viper PST w/ a FFP. I just got a 4-16 Viper PST but have not received it yet. My son and I will be hunting with these scopes at 600 yds. this September. I'll have a better side-by-side field comparison then.