In a nutshell, the major hurdle with WM6.5 is memory. Anything that impacts memory is going to make a difference.
Easiest improvement is probably using a ROM with no camera (so-called "high memory mode.") But I use my camera.
Next, dont install 72 Titanium plugins. (imho they're not that pretty anyway.) I'd have the honeycomb as my main page if I could, except I miss checking the weather.
If your mem is at or above 20 megs, you're fine running Opera. Even w DCD's ROM I exit SPB Mobile Shell to run Opera at its best. Man Opera is nice, almost iPhone-like.
I'd also remoe stuff from /Windows/StartUp you don't need, like RSSHub, and whatever else you don't critically have to have on all the time.