People shoot 1,000 with fixed 10's.. I have a 4-12 on my 22-250 and stretched it to 1,000 on no wind days.
It's not necessarily bad to run to the edge of scope adjustment, as long as it tracks then it's no different then being in the middleof adjustment. With some scopes and a 20 you could end up on the upper end of adjust just to get zeroed.
20moa bases cant the scope down in the front, the longer the scope, the longer the scope the better odds you have of needing taller rings. If you like to run your scopes as low as possible then you may need to switch bases to clear the objective lens. on ARs, chassis guns with full shrouds or big crazy bull barrels it's more of an issue. All of my rifles have 20 moa rails..
Bottom line for my recommendation: if 1,000 yards is "long range" for you. 20moa rail is not needed but if you want it, get it.