I think the difference in performance in the snes version is overstated. The snes version was fine, I never played the game and thought "how unplayable this is". The fact that the snes could even handle Street Fighter Alpha 2 later on (despite the fact it was very stripped down) shows that it was not a machine as slow as everyone says.
Oh it's certainly not unplayable and I had a massive amount of fun with it as a kid, but if you play the arcade version of SF2HF and then play both the SNES and Genesis versions, the SNES version's timing is a bit off and there is very slight slowdown during fireballs and just in general. The SG port on the other hand has zero slowdown and you can pull off every single combo, CPS1 chains included, that you could in the arcade version. I'm no SF2 expert but the SG version has zero slowdown and perfect timing while the SNES version looks better, arguably sounds better but has just a tiny bit of slowdown. It's still a great port though so I was by no means calling it unplayable.
Super SF2 is one of those games that I see as superior on the SNES simply due to the SNES' sound chip and its ability to replicate the arcade version's music/sounds more accurately, although the SG version actually has the full arcade voice samples, just really really grainy. The SNES version's are often cut or even totally different, but they're clearer(although muffled) and the music is fantastic. SG version has less slowdown still, but the SNES version of Super simply feels more like the arcade version due to its superior colors and sound.
The SNES Alpha 2 port is indeed impressive, but to be fair it does use the S-DD1 enhancement chip.
Rust: I usually just set the turbo setting to 3 or 4 stars to make it the same speed as the arcade or just a tiny bit faster. Setting it all the way to 10 is kinda funny and all but it makes it nearly impossible to play.
OT, but I would've loved to see more SuperFX-2 games on the SNES that used the chip to enhance 2d sprites like Yoshi's Island did. That game is breathtaking visually and looks better than many early 2d games on the PS1.