I believe I test rode the Aluminum and the Pro, and for me the
shallower
head tube angle on the Pro was more comfortable.

I like to stand up and climb hills and lean quite a bit forward when I
do and the
72 vs 73 felt more stable to me.

I think the head tube angle may be one of those things where they
shift it o 73 or more and it's not best for a lot of people but a lot
of ppl don't know because there's hardly anything else on the market
anymore.

I've got an '04, but you're saying the carbon version head tube is more
shallow than the alu version? I think mine was a 72 also. Makes steep
descents not as hairy, being more upright, with the shallow head tube angle.
It does take some getting use to. I didn't like the wheels my Roubaix 105
alu came with. I put my wagon wheel rolf wheels on it, and it really
started sailing. The other wheels seemed sluggish to me, don't know why.