In my experiences, you don't really lose any performance running a 32-bit OS on a 64-bit CPU. Consumer 64-bit CPUs are made to be compatible, able to run in either mode. So you won't suffer a performance loss versus running a regular 32-bit CPU at the same level, you just won't gain the extra performance you would if you ran a 64-bit OS for your processor. The tradeoff is that things will work just as you expect them to.