Most games will be fine with an 020 and RAM.
A lot of people like an 030 at 50mhz. That will speed up hard drive access and you are about 5x faster than stock A1200.
A small number of apps and games will take advantage of an 040 and 060. But they are pretty rare nowadays.
I assume you want to keep it retro and not want to run modern apps on it?
Check this link, under A1200 accelerators:
http://www.bigbookofamigahardware.com/
