The reason for 20 moa and even 30 moa bases is that certain scopes were not designed with sufficient travel in former times to allow for shooting at very long range.
This was essentially a stop gap measure to all scopes to move from shooting at ranges from 100 to 800 yards to say 600 to 1200 yards.
Most modern scopes allow sufficient erector travel to all shooting in excess of 1000 yards. (A practical limit.) without special bases.
In my opinion, if you buy a scope that has more than 40 or so MOA of elevation, you shouldn't have a problem with most conventional calibers.
Check your ballistics tables for your round and see. This was a issue of particular interest with the old design Unertl 10x M40 scopes.