In my experience, Mesa preamp tubes are not very smooth. I've had great results with vintage Tung Sols and Sylvanias in terms of smoothing out the gain in my Mark IV. I also installed a new Mullard 12AT7/CV4024 in the phase inverter of my C+ that really helped tame the beast. The 12AT7 is a lower gain tube, but in the PI it didn't cut the gain very much but made it more musical. YMMV.
