As you can see, the Daytona Coupe would top speed limited (based on 6500 rpm max):

TKX (0.81): 5th Gear - by gearing at 173
TKX (0.63): 5th Gear - by gearing or drag (can theoretically hit 200 mph at 5850 RPM in 5th)
Magnum XL (0.50): 5th Gear - by gearing (at 190 if you could do 6500 RPM) or drag in 6th gear
Magnum XL (0.63): 6th Gear - by drag (could do 175 in 5th gear at redline, shift into 6th and drop to 5100 RPM and accelerate to 200 mph at 5850 RPM)

Overall, it seems the TKX (0.81) probably makes the most sense for a 5 speed street driver since not many people will ever use the true top end of this car (and "only" 175 mph is fine for most). Beware though, highway cruising will be pretty high RPM.

The Magnum XL (0.63) seems to make the most sense as a 6 speed street driver since it allows the full potential of the car while keeping revs manageable for normal use (2050 RPM at 70 mph). It seems to have the widest range with the closest spacing.

The Magnum XL (0.50) version has higher top speeds in every gear (except 4th which is direct drive in both) but that 6th gear is really tall... 1600 rpm at 70 mph.

Lastly, the TKX (0.63) is identical to the (0.81) in the first four gears and then, of course, has the taller 5th gear. The difference at 70 mph is 2050 RPM and 2634 RPM. Hmm...

So... in your real world experience... what are you TKX owners liking, the 0.81 or 0.63? How much of a concern is the highway driving... i.e. do people drive theirs much on the highway? Do 0.63 owners hate the large spacing between 4th and 5th?