Tremec TKO500 vs. TKO600?

I just got the TKO 500, I would have gone with the TKO 600 but I just bought a clutch and didn't have an extra $300 to shell out. What is the big difference. From what I have read, the TKO is the same except different gear ratio's and only comes with the 26 spline input shaft. If I were to get another clutch and then buy the 26 spline input shaft would the TKO 500 be just as strong as the TKO 600 but with lower gear ratio's?

This has been bothering me.

I should have called first but in case anyone was wondering...

I called Tremec's tech line and the guy said the only difference between the 500 and 600 models is that the 600 only with the 26 spline input shaft and the first gear is higher, besides that the materials and internal strengths are exactly the same. So by getting a 500 with the 26 spline input shaft you are getting a 600 with a lower first gear. He also told me the 500 is good for 575 tq, which I am no where near and if I ever get to that point I would probally go with an auto anyways.