512k is just about all you'll ever find for these, even a 256k should help out. 1-meg caches theoretically existed, but I've seen maybe two or three accounts of them "existing" and "being used" in real life. Any cache and all should put a bit of pep in these machines' step, too.
The other thing I recommend that should help a lot, especially if you run any 68k software, is to install Speed Doubler 8. Among other things, Speed Doubler 8 has a replacement 68k emulation code path which significantly speed things up. The boost can be
huge. It's enough that a 6200 (with its 16K of L1, which is the best theory as to why the 6200 did poorly at 68k emulation) goes from 10% of the speed of a Quadra 700 to around 150% the speed of a Quadra 700, in "general" tasks. (It's still bad in floating point specifically -- but so are all PPC Macs: the first Mac to be faster than a Q700 at floating point was the 533MHz digital audio, so that was always a weak point.)
(in 68k benchmarks, 6100s start at around 50% as fast as a Q700 at general 68k emulation, but SD8 should still boost that a fair bit.)
I'd say, keep up the search for the cache card. I've seen lots of great work on memory replication too so it may be possible that there's enough demand to justify new ones being built, that may be something to check with SiliconInsider on.
Prior to "G3 upgrade" or "Just buy a faster Mac
" caches are some of the best speedups for this era.
The LC I/II/III aren't affected.
Good to know! I haven't ever had an LC III and the last LC I had was in ~2005 or so when I was still puttering around with chaining double-A batteries together to replace PRAM batteries -- which, worked well! but, at this point I'd say not to bother with PRAM in anything except Macs you'll pull apart frequently and don't trust to do the PowerToggle on.
With a power supply from 1993-1995 I'd say "hmmm, best not to risk it if you can avoid it, especially all that often" which is why the last time I used my 6100, I just let it run for weeks on end. It'd probably need a recap before doing that today, though.