I hear you; I have a co-worker with a very nicely running 2.1, which also ran perfectly on 1.5, as mine did. She won't root and is happy with it as it is, so we did some comparing:
Both devices shut down and left off for two full minutes, then started (we did not actually time the boot ups), mine was finished for at least 15 seconds before her's was.
First test was hitting "phone" and making a call to my other line, a Blackberry 8330; no speed dial allowed. I had the keyboard up and had entered the entire number and had just pressed the "call" green button just as her keyboard finished coming to the screen.
We performed three tests, but my favorite was the "menu test." All we did was hit "menu" at the same instant on our way through the sub menus to "manage applications" and menu again for "sort by size." It was hilarious, her non-rooted Eris was still doing the original sort, before the icons appear on the left of each app, when mine was finished and I was standing there looking at the sorted by size applications, scrolling down, etc.
"You're cheating," she said, "yous is overclocked."
Yep.