You're not going to make it to 500 with a 40MOA base, and if you find a 50MOA rail, you may well not be able to dial down to more typical closer ranges, and even if you do the scope will be pretty jammed near limit of travel.
The Viper PST has 20 mils total travel, and [should] come centered so you could dial 10 up, 10 down (figure you'll gain or lose as much as a mil for zeroing).
So, if you add 11.8 mils (40MOA rail) to that baseline 10 mils of "up," you get 21.8 mils. This should get you to 400 yards or so. You need another 9 mils to get to 500... and then, would you be able to zero because you're out of "down" and the erector is at or near the limit of travel, straining the mechanism?
I have a 5-25x50 Viper PST mounted on a 20MOA rail on a CZ-455. It runs out of elevation at 14.1 mils, which gets me to 300ish yards. My Vudoo has a Gen-2 Razor with 28.5 mils of total travel on a 30MOA rail, and it runs out of "up" at 16 mils or so (325 yards).
I haven't shot a rimfire match that ran more than 300 yards, and those really long shots were far fewer than the more typical targets. I'm happy to use holdover for the longer shots and not have to jam the scope erectors near "down" limit the rest of the time.
My $0.02.
Edit: I guy I know bought some brand of adjustable mount which allowed him to "dial" something like 70MOA of elevation in addition to whatever the scope had. But the tracking consistency... yeah, he didn't keep it.