I have the R600 and before I bought it I called Shimano and they said the only diff is the weight of the chainrings. Both use the hollowtech crank arms. And basically it's the 105 level crank, like mentioned earlier.

I installed it on my 9spd double w/ the Ultegra BB and I like it a lot. It's sweet and once I adjusted the FD and RD everything shifted fine.

So I figure once those wear out I can replace them with the R700 chainrings if I care about weight.

Crap: That's not on the reg PBK website under chainset! I had to do a search and it came up. I thought I got a good deal off of someone on craigslist! Crap! That is much cheaper with no shipping too! R600 PBK linkj