I just switched from the TKO 500 to the 600 with those ratios and a 3.91 out back. I don't notice the difference in first much, but I like the closer ratios (1st through 4th) on the 600. The taller 5th gear is a little better on the highway. I can cruise at 80 all day. It is a bigger step from 4th to 5th, but even on a bigger road course that's only one or two shifts per lap. I vote for the 600.
