The 6500 doesn't use 72pin simms, it uses 144pin dimms, just like the 7300-9600 macs, sometimes they can even use the same sticks. Also, the max on a lot of the machines is 136mb, mainly because of the 8mb that was built onboard.

I'd take that machine all the way to 7.6.1, it'll run IE5 (the best-written browser for classic Mac OS) just fine, and everything will fly, you'll be able to turn VM off, which is also a performance boost when you have enough physical memory.