This. A lot of the OS recommendations on the Garden are inaccurate because most people do not use System 6 so they just leave it unchecked when uploading files.
Back when I had a place to put it, I ended up putting System 6 on my IIsi, because I couldn't get System 7 to run as well (there was some video choppiness in After Dark and elsewhere that I couldn't get rid of under 7, but it was mostly nonexistent under 6).
This was with the full 65 MB of RAM, too, so that wasn't the problem, and I don't think the disk had anything to do with it. Overclocking the CPU might've helped some, but I didn't really feel like bothering, because there wasn't anything I wanted to do that 6 couldn't handle and it was otherwise plenty fast since it was the IIsi's stock OS, so I just left it alone.
I also managed to track down copies of Maxima and Optima, and one of them (I can't recall which) enabled access to the full amount of RAM beyond 8 MB under System 6, which wasn't especially useful, but it was nevertheless fun from a "Because I Can" perspective.
c