2.1 Will be slow to start with as the phone has to re-cache everything. I'd say give it a week and see how it goes, in my experience 2.1 is alot faster and smoother than 1.6 once it gets going. Just a suggestion
Luster White X10i >> Debranded (Uk Generic FW), Running 2.1, Rooted with z4Root, modded Framework-res.apk and various system APKs, more apps than I know what to do with but I still cant make the damned thing make the dinner...
Give 2.1 a chance to settle in and build the Dalvik cache, also there are mods and hacks you can do to the phone to make it much faster if you don't mind rooting your device.
Posted on my X10i using Tapatalk Pro and Swype Beta