No, I wouldn't want its clean channel to break up. I have other amps that do that.
Hey, we're all different, right? We want different tones.
Some Mesas have clean channels I dig - the Lone Star is one - and some don't. On the other hand, I don't love the dirty channel on the Lone Star at all, and yet I bought one even though I have yet to find a tone I really like with it.
And one of my favorite amps of all time was my old Tremoverb, and I wasn't crazy about its clean channel either. I sometimes get an amp just because it does certain things I like, even if it does other things I don't love.
But the clean channel on the Custom 50 sounds even better to me than the clean channel on my Lone Star. That's the amp I wish I'd bought instead.
I think I just love the tone of PRS' cleans more than Mesa's cleans. Nothing wrong with that. At some point I'll get a Petrucci amp just for its Channel Two. I really like that, it's different from my PRS amps.
So, Les, you could sell that Lone Star and get a Custom 50 head and not have to deal with a 90lb amp! Of course, the Mesa is probably on wheels, but I bet you like to get it off the floor.
So far, my experience with the Custom 50, is that the clean channel is one of those tones that just makes me go, "oh, yeahhhhhhh" every time I play through it - and I'm not even using the recommended speakers at this point. It's a warm, lush tone that can work in a good amount of sparkle, without sounding harsh. It's got a lot of bottom, but nicely tuned, and makes it easy to add a tubescreamer without getting instant tinnitus. Plus, something I notice about both my PRS amps is that they have a clean tone similar to and just as instantly satisfying as a good Fender, but have more midrange available than most Fender amps, which is nice to have access to.
I'd be interested to put the Custom and a Lonestar side by side and A/B the drive channels. To me, it sounds like the Lonestar has a very American inspired crunch tone, where the Custom has a little bit of Marshall influence and perhaps some of the Mesa Mark series in there too. It's no clone of anything, but it can get close, especially playing with the mids, and the subtle, yet useful, mid shift, which can add or remove girth from the low mids. Some people say it's got a modern, metal and heavy rock vibe, but I don't totally buy that... well at least not with my current speakers. It doesn't have the tight, low end thump and blistering bite of the Rectifier or Archon flavor. It certainly has cut, but it's warmer on top and looser on the bottom. Probably something a Mark V could emulate more so than a chug machine, but here I go again talking about amps I've not tried.
I had also been pondering a Mesa Stiletto Stage II, and that probably isn't over, but I'm glad I got the Custom first. I think the hot, JCM tone would be right up my alley, but I highly doubt the clean channel would come close to the Custom, nor would the amp be as useful as an all-around tool. If I've got to haul an amp to gigs, I want to love all of it, not have to face a compromise on one channel.