I have the exact two amps you're talking about in my rack--old blue LED 2:90 and the new silver knob 2:50.
It may seem obvious, but just one side of the 2:90 is incredibly loud. The headroom is awesome if you plan on using the deep switch, or just tune low. My impressions are that it has a bit of a mid spike because of the simulclass--similar to the Mark IV maybe--so it may match well with the Studio preamp.
The 2:50 on the other hand is cool because of switchable bias. To me, this one sounds exactly like the power section out of rectifier. Might be a bit brighter too.
Also, if weight is of any concern, the 2:90 weighs almost as much as a whole head.