I run the TKO 600 behind a warm 496 wedge. Street and road course. I have been happy with it... cross country and on the road course.

With this transmission, you have a choice of OD ratio. ~.81 or ~.65. On my setup, .81 makes a perfect top speed gear and .65 a perfect fast cruising gear. I went with .81.

A 6 speed reduces the trade-off... you can have both a top speed gear and fast cruising gear.

There is also strength to consider. After freshen and tune-up my torque is pretty well maxed out for the TKO600. Any more and I would need something stronger.