Here's the comparison of SR600 to SR400 frame specs:
SR600 / SR400
Seat tube angle: 73.7 / 73.7
Head tube angle: 74.25 / 73
Top tube length: 22 / 22
Chainstay length: 15.75 / 15.75
Fork rake: 1.5 / 1.5
BB height: 10.75 / 10.75
Wheelbase: 38.48 / 38.9
Trail: 2.2 / 2.5
Ground to top tube: 31.9 / 31.9
BB to top tube: 22.07 / 22.07
I don't know what some of these mean but there are some minor differences. I don't know how large a difference these minor differences will make though..