I can confirm that L3 makes "all the difference". My son has a quicksilver (actually a DA logic board), overclocked to 150MHz FSB. The 1.5GB ram is running CAS2 at that speed, and GeForce 4 Ti graphics under OS9. I think this is pretty much the fastest possible setup.

For a long time, I was running a 7447 @ 1.5GHz (512k 1.5GHz L2, no L3) but I was still experiencing lag in a few of the more demanding SuperNintendo and Gameboy color games we play (Kirby and Shantae spring to mind). Anyway, I got tired of the fact that I couldn't sleep the machine no matter what combination of 3rd party enabler/multiprocessor plugin/energy saver settings I tried.

So I put in an older OWC 7455 clocked at 1.2GHz (150 x 8 ) with 2MB SDR L3. As expected, sleep now works great! However, what I didn't expect was how much faster the emulators were... It was night and day. Games which had been glitchy and dropping down to 45fps now run consistently at 60fps, flawlessly. I really didn't expect this because the L3 cache is running at 5:1, or 240MHz... That's only 1.5x the RAM speed (and CAS 2 dammit!).

Maybe OS/X is different, I don't know. As it stands though, for me in my ultimate-retro home-theatre (1360x768 37" : ) setup, a 7557 with L3 would be epic.