I have my spr all built (18"), totally done except the scope. I have been looking between the Vortex Viper PST in 2.5-10 and 4-16 in MOA with the second focal plane. the 2.5-10 has no parallax and the 4-16 does. I think 4x on the bottom is a little too high for a fighting rifle but thats just my opinion so far. All I want this for is for a SHTF gun and yotes. I would like to shoot to 600yds and hold MOA to that distance. I know the 4-16 is better at 600 but that will be the exeption not the rule. Also if there is some other scope that I am missing here that I should look at then let me know. I dont want to really spend over $1k for a scope and I dont want to go down as far as a 1-4 so let me know any other suggestions. I think if the 2.5-10 had a parallax I would just buy that. Let me know what you think.