Convince me to put a TKX in my Dart
In my mind having OD split into 2 gears is only useful if you have short enough final drive ratio where they will be used under power and you don't want a big RPM drop going from 1:1 to overdrive.
I don't disagree, to a point. As an example, the TR6060 I plan to run has a 0.50 6th gear. I would not want to go from 1:1 to 1:0.50 in one shift, under power or not. At the same time, a 0.68 5th still isn't enough of a drop for me even with a 3.55 rear gear.
I think the overall combination has to rule. The TR6060 with a 0.50 6th put my 2015 Challenger at 1500 RPM at 65 mph. The motor was fine there, ran smooth and pulled the hills without needing to downshift. But the OP's motor (I don't think) would be happy there and 6th would only be useful at 100 mph or something. For him, it makes no sense to run a 6 speed, he can't use the lower RPM. For me with a mostly stock 5.7 (someday), a 6 speed makes much more sense because I (should) be able to cruise at that lower RPM.
The other thing to look at in these transmissions is the ratios and RPM drops between the gears. In that regard, a narrow ratio TKX (2.87 first gear) and narrow ratio T56 (2.66 first gear) are probably going to feel pretty comparable. But the T56 might have the edge in the RPM drops as it has a better spread 1st-3rd and 6th gear cruise RPM will be lower. No idea if the difference could be felt though. The wide ratio TKX will probably feel much stronger in 1st-3rd compared to the others but will add RPM on the highway.
For what it's worth, it looks like the wide ratio TKX is almost a match for the TR3650 that came in the New Edge Mustang GT. So if you can find one of those and test drive it, it should give someone a good idea how that TKX would feel to drive in regards to gear ratios and RPM drops. Except I bet the TKX shifts better.
