I don't recall much of a speed difference between running 7.5 vs 8.5 on our 6200. Actually, I don't recall us having any problems with it at all. I know everyone else thinks they were such terrible machines, but for its time, our first Mac did what we needed it to do, and made enough of a good impression on us to keep buying Macs.
I remember that the monitor we got with it was a big problem for us... Multiple Scan 15, I believe. They would develop a case of the blues... literally. After the replacement one (through extended warranty) did the same thing, we went with a generic PC monitor and the appropriate adapter.
The 6200 still works, but sentimental reasons prevent me from parting it out. It's currently serving as the bridge in my 'get needed software from newer Macs to older Macs' restoration efforts. Hopefully, once I can find some SCSI hard drives that don't cost an arm and a leg, I'll have an ethernet-ready Mac and won't need that extra step.