My experience is that Tiny Terror can keep up with 50 and 100 watt amps in most situations. Cab size and number will be the determining factor. More speakers = more volume. I have have used it in Jams and even at a DRG Jam with other Dinos from the forum, and I've found that through a 4x12 cab, it keeps up 90% of the time.
At Jams
At jams, I've run it through a 4x12 and left the Tiny Terror on the 7 watt setting. I wanted to see how minimal I could run the thing and still keep up. At 7 watts and at half volume, it was loud as hell, and easily kept up with a very heavy hitting drummer. I still had the top half of the volume knob I could have gone to, and/or, I also could have kicked the Tiny Terror up to 15 watts. So I don't think keeping up volume-wise would have been a problem, regardless.
As good as the Tiny Terror sounds at apartment volumes, like any good tube amp, it gets even better the more you air it out. It really does that classic
It totally shined on everything from clean funky rhythms, to screaming harmonics and dive bombs, and it sounded great on all of them. I was getting feedback with ease. With my back to the rig, all I had to do was to a quarter turn, and the feedback came immediately. It responded great with all my pedals, particularly the Phase 90 (really fat) and the Tube screamer was perfect for kicking up the lead work. It was a real pleasure to play with something resembling MY sound again, as opposed to just a sound.
In Bands
If you're the only guitarist in a band, the Tiny Terror will work most of the time. Check this clip of the Tiny Terror at full volume with a band at 5:42 of the video. Pretty decent proof of concept.
http://www.youtube.com/watch?v=P-PHqs4zBAc
If you're in a situation where you're in a band with other players running their 50 or 100 watt amps full out, you won't keep up. Get a 100 watt amp for that. But how often is that? In any live situation where you can mic your cab, you'll likely be fine.