RacerTex: Usually the arm problem you had there (with GM3s, at least) is caused by overheating or strain on the armature. While I wouldn't say that a 26/72 combo on a TC3 would be excessive, it could still be a bit high, especially if you were running on a tight, technical track (your ratio was a 72/26 * 2.5 = 6.92).
On a tighter track I would run a GM3 in the 7.2-7.6 range, on a more open one I could see going as low as a 6.8 or 6.9. I usually try and play it safe though. Not all GM3s will blow like that, but it is definitely a more problematic motor than some others and is more sensitive to heat/strain than, say, a P2K.
Right now I have a 7.32 (final drive ratio) in my XXX-S and it is plenty fast.