So if I want to ride 68 cm saddle height at 140 lbs, I'd set it up around 68.5 cm, which means I would not to cut around 1 cm off the seat post carbon which I assume can be done easily with a hacksaw. Reach is only 1 cm longer than my P3, so 1 cm shorter stem takes care of that.
I'm kind of in a similar boat. I'm on a small Shiv with the aerostem set at 65mm. The reach on the Dimond is 2cm longer, but no one makes a 65mm stem. The Zipp Vuka Stealth, or Pro Missile Evo seem to be the best choice. I really like the Tririg Alpha, but I don't know if I can get the pads back far enough to match my current pad reach.