I don't think a 3.73 is enough. That moves the RPM's up less than 200 at 70mph. I think something between a 3.90 and 4.11 would be good but the problem once you get up to a 4.11 is that first gear gets so short. That big drop between fourth and fifth with the TKO-600 puts you from on the cam to off the cam in normal street driving scenarios too easily to me and is really the only issue I have with this trans but it is a friggin' jet out on the highway. You know, the TKO-600RR would be a good one with your gear if you didn't already have the regular 600.
This is the "problem" with the trans...the huge space between 4th and 5th. I could be driving at 2500 in 4th, shift to 5th, rpms drop to 1500, and the motor doesn't really like it. You have to deal with this space no matter what your rear gear is, cause all your rear gear does is move this "space" up or down. I'm running 3.90's now, will likely go to 4.11's as my ring and pinion are messed-up anyway. However, there wont be a big difference from 3.90 to 4.11's.
Question is, how do you use the car? If your around town mostly and want to use 5th, you need to install a small cam, and get some gear in there. Highway, you can run just about any cam, so long as you get the rpms up over 2000. Mine purs at 2000-2100 at 70 on the highway.
If I had to do it all over again, probably run the .82 RR unit along with a 3.55 to 3.73, and enjoy another "evenly" spaced gear drop from 4th to 5th. Probably would get better mileagle as I'd be in 5th all the time around town, rather than screaming in 4th, lugging in 5th.
PS - dont worry about teh too short first gear thing...its supposed to be short! Stick cars like gear, about as much as you can throw at them, as there's no convertor here helping out...its all muscle!