T-45 Tranny is by far the best and can easily hold 600tq.
......oh no wait, my bad, I mistook it for a real transmission. The T-45 is good for taking sh#ts in and using as a tissue box, but thats about it. Damn weak precious little tranny breaks down more often then a Civic motor with 15psi of KB blowzilla boost.
I think some t-56s are rated for higher torque, like the tranny in the Viper for example. Besides cost, t-56 are heavy too. If I remember correctly they weigh like 100lbs more that a t-5. I would be considering a tko like neoclas suggested. Of course if I suddenly found myself suffering from hypogonadism, and could no longer make my keyboard levitate at will, I'd consider a built c-6.