My original Streak came with 1.6 and was updated to 2.1 and then 2.2 and finally another update that really killed it and I returned it to Dell for a new device. My device is Kernel 2.6.32.9-perf Build 15697.
To be honest, nothing after the first 2.1 update seemed to be an improvement, although my new device seems fine so far.
I don't plan to update unless it goes to 2.3 or 3.0.