Obviously, if you think the Classic environment is too slow there's nothing that anyone can say to contradict this. Since it's a matter of perception, I can't say that you should percieve it faster :-)
Think of Classic as an "above and beyond" sort of step. Apple has provided the API continuity for developers with Carbon (which is roughly akin to what Microsoft offered to get apps onto NT) and then they went one step beyond and offered the full older OS but placed in a nice little compatability cage so that it couldn't kill the other "well behaved" apps on the system. It even went one step further than that and made the two share the same screen and some of the same interface elements. That's a big feat in my book.
With that said, I'm not certain that I want to run Classic on my machine. I don't want ANY app that isn't built upon carbon or cocoa and it'd be nice to have a way to keep from accidentally launching the Classic mode since I don't want the compatability and I don't want the performance hit.
I did have a great idea that Apple should port the emulator for the old Apple //gs to the Mac and have it run in a similar way to Classic ("green box?"). That'd be impressive that they can now offer backwards compatability for customers since 1976 and might even be helpful for a few schools who still have to rely on old, out of date machines because they can't get decent software budgets even if they had hardware to upgrade.
The whole subject of compatability is a fascinating one and though I will make sure the apps I use don't rely on the compability boxes, I think that Apple has gone above and beyond the call of duty with what they have offered end users in Mac OS X.