Conventional logic would say Streamliner 600 with the Thunderchild 112, and 900 with the 115. However, I tried a 600 with my TC, and it hit the yellow light a little too easily for my tastes. It compressed on big hits in a way that I found disappointing in comparison to the 900. I really liked the open, effortless headroom I got from the TC112AF/SL900 pairing. The big Streamliner's are the best high-passed and limited 900 watts you'll ever run into. I flashed the yellow light once in a while, enjoyed the "tube give" of the limiter, and yet nothing bad happened to my Thunderchild. It's a tough little cab. That said, you do have to be careful. I ran the low end a lot leaner than most people do (220 mids cut, not boosted, and bass at 9 o'clock), and I have good dynamic control. It all comes down to "know thyself". If you tend to run whatever you have to the max, no matter how loud; if you are heavy-handed; if you've blown cabs in the past; if you use a lot of compression (sustained wattage instead of brief peaks), then the 600 is a safer bet.