Our 2003 9-speed Ultegra brifter finally packed it in last year. I had some 10-speed Ultegra stuff squirrelled away against this event. I only changed out the brifter. The 10-speed brifter did shift the front sort of OK, but not really, with lots of missed up-shifts. I put up with it for a while because I wasn't sure of what else to spend money on. The old rings were worn, so I put on new 10-speed rings. Essentially no better. A couple days ago, I put on a 10-speed Ultegra FD and chain. Bingo. Shifts perfectly, including on the 9-speed cassette. The 10-speed FD is a vastly nicer and better made piece of equipment. So at least now we know that 10-speed Shimano cranksets are identical to 9-speed cranksets. No other way to tell as the specs are not published.

I'm running our last nice 12-34 cassette and I don't think there are any more..When that wears out, I'll replace the right brifter with a 10-speed and put on a 10-speed 11-34 cassette, which will work fine with the old XTR RD. I think 10-speed chains and cassettes will be around for a while, no need to stock up yet.