Will you be playing lead or rhythm. It's just my opinion but, I believe a lead guitarist needs a tube amp they can drive into breakup. If your fellow guitarist is playing rhythm with a 50 watt I'd look at a tube amp in the 30 to 36 watt range. It will break up at a volume that would compliment the rhythm player at comparable volume levels. If you're going to primarily be the rhythm player and you lead guitarist has a 50 watt amp I'd be looking for a cleaner amp between 50 and 80 watts or even up to 100 watts. Watts in a tube amp have more to do with how long it will remain clean before breakup. A Vox AC30, (approx 36 watts), dimed will be as loud or louder than a 60 watt Fender played clean or crunchy.