I recently attempted the replacement of the crystal oscillator on a SuperFX SNES pcb, specifically Stunt Race FX. I followed the method described and illustrated here:
http://forums.benheck.com/viewtopic....asc&highlight=
I got the 18pf capacitors however I used a 25mhz oscillator. First, I soldered in the new oscillator and tested it and it worked fine although I could not tell much had improved. I then put on the capacitors and from there my cartridge glitched up. The video was completely scrambled while the audio was intact. Once in a race the controls ceased to function at start was also an issue.
I removed the caps and all was well but still the net gain of improvement was negliable although it seems others have no need for caps either.
Basically, anyone else who has done this would be whom I'm speaking to. What sort of improvements did you see when you replaced X1? I suspect as addressed elsewhere, the game simply runs smoother, not faster. Parts with slowdown are lessened but the general speed is not improved or exceeded from the previous.