Well, as far as my research shows, yes UB is slower than most, but it is not horrible by any means. Here's a link to that thread:
http://livepokerforum.com/forum/viewtopic.php?t=2972
I do mostly play $2/$4 at UB now, but the bulk of the bonus that I've earned thus far has been at $1/$2. It may also be because I mostly play O8 - which usually has a higher pot average (and therefore more rake).
Still, I mostly choose UB as a good second site. If it isn't for you though, I can't argue.