I actually use Tweed most of the time now. I need to be able to keep the volume down, and at this point Tweed gives me a good enough level and still lets me dial in some good mojo. I'm using 6V6s and EL34s.
In my 1st show with my new LSC, I freaked out trying to get a good clean on Tweed on a big stage in a big room -- wasted sound check trying to deal with what seemed like a sudden failure of what had been a perfect setup during rehearsals. It quickly turns to mush at anything higher than moderate levels. I was bummed... until I remembered that I was using the Tweed setting, and I never had the problem again.
So it isn't good for any amount of really clean headroom. The cleans will break up at anything beyond the levels I play at usually. When I do run into mushiness, it's easily solved by just switching over to full power, but I haven't needed to do that for a while. Most of the time it's just perfect, juicy furry cleans and a great saturated drive.