I own both .... neither are for sale. These are my favorite's of all the Mesa amps.
A amp with the clean and lead channel of the IV and the red, orange, blues channels from the Tremoverb would be nice.
The lead channel from the II,III and IV is a classic. Maybe the best hot Fender sound ever made. People that play very different have used this sound (Stones, Metallica, etc, its a big list) The cleans on these amps are very good. It is one of the most versatile amps ever made.
I have played on amps with more gain and/or bass than my Tremoverb but I feel none are as aggressive after doing a direct A/B with. Diezel, Bogner, Rivera, Engl, Fryette, 5150 etc all are great amps .... but I feel all sound kind of polite in a direct A/B.
I remember Ed DeGenaro asking me if I use the the red channel and him telling me "It's too much for me".
It also is very versatile .... I can get in the ball park of Fender and Vox sounds. The clean and blues channel does a pretty good English crunch sounds. (something the IV does not do very well).