Ive run a stock auto box with Hi stall at over 650 and absolutely caned the car with no problems, the weak point is the 2nd gear sprag this will ALWAYS let go unless changed so any box without this is only a little stronger than stock, the BL boxes when stripped have virtually nothing done to them but do seem to be 'blueprinted' and have different clutches fitted, TBH the Titan box is little different but then again its not hard to make a box that stock will take 650 hp if its cooled take a bit more as the stock box is engineered to do 100,000 miles plus and we prob wont put 10,000 miles on a box and only a small % of those in very high power state.
I do know what the box Lee used at SRD has done to it and that WILL take much much more abuse than ANY of the US boxes, the trans builder is used to building very very hi spec boxes for drag cars. But if you wanted the ultimate in quickshifting and unbreakable you would need to go TH400 with gear vendors overdrive or a GM4L80E which can be modified to reliably take way over 1000 ft lbs of torque.