I went with the IA10

Cheaper, easier to work on, throw on a tririg front brake, and pretty damn fast.

Bars are more adjustable on the IA10, which makes it more likely you will get into your fastest position.
Most 'superbikes' aren't very super because they don't facilitate this.

Go with the 10 (like I did) keep the cash and buy a power meter or upgrade the wheels....I vote for power meter first (but you didn't ask that) :)

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"see the world as it is not as you want it to be"

IA10. I like Di2 more on a TT bike because of Synchro and because you can hide the install better tan eTap (the blip is huge). The IA2 is a $2,500 premium. But, you will spend some of that on Tririg brakes and Tririg cockpit. Then, you will have $1,500 left over for killer wheels or whatever.

I went with a NOS FRD frame, which is basically the same design as the IA2, just different carbon.
My decision was based on:

1. I really like the look of the hidden front brake. I don't believe there is any real aero advantage to it, I just really prefer the way it looks.

2. If I had bought the IA10/16 I know I would have wanted to upgrade to a higher end aero bar, so that would have been another 1k. And then I would have put a tririg front brake on, another $200 or so.

3. Everyone always says you'll get a faster position with the more adjustable bars on the IA10.....well, the 'integrated' bars on the IA2 are still pretty darn adjustable. I had no problem getting it to my stack/reach numbers with room to spare in every direction.

4. Because it was a NOS frame, I got a steep discount on it. No way I'd pay MSRP for that thing!!! I know there were lots of IA2's (or 3's? the orange ones) on sale last year from multiple dealers. As were the IA16's too.

Seems like the IAxx has more of the votes from anyone I've asked

Biggest relevant difference is that they fit differently. IA2 will be lower than the IAxx

Pretty sure you have that backwards?

Stack for a 54cm IA2 is 52.2cm

Stack for a 54cm IA10 is 51.3cm

Super dave i think it was addressed that before. Because of how the integrated bar and stem interact, the IAx will have a lower stack. I could be wrong, but I'm pretty sure i remember reading that