I've been considering purchasing the Stages PM in grey, 175mm, Ultegra 6700, but unfortunately I've waited a bit too long to pull the trigger. They are out of stock. I just called to check if it is on back order and when available, but I was told they have discontinued making any more 6700 PM's. Silver is still available, but not grey. Stages did indicate that the 6800 crank arm PM would work just fine, with a little difference in aesthetics. That appears to be the only option for those that want to go this route who have 6700 cranks.
Is there any issues besides the minor difference in aesthetics with mixing a 6700 crankset with a 6800 crank arm PM? Will the minor difference in the crank arm weight affect the functionally of the PM? Any other issues to be concerned about?
From what I found when I asked a similar question a Stages PM works the same no matter what crank it is attached to. It is measuring the flex of the crank arm it is glued to and the rest of the crank has no impact on the accuracy.
The response I got from Stages is -- "The 6800 is completely compatible with the 6700 crankset, as it attaches the same, and the color matches identically." They also stated that the 6800 PM crank has a clearance issue with some bikes, such as the Trek Madone, where the sensor rubs against the chainstay. Apparently not a problem with Giants. My shop mechanic didn't think there would be any issues either.