Which TT bike seems like the better buy?

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I've been doing sprint and olympic distance dus for several years...quite possibly my favorite way of combining my 2 sports. I can hold my own on the bike and it's definitely my stronger leg, but quite often I wish I had a dedicated TT bike. I can ride in the drops for a fairly long while, but after busting my right wrist in 2 spots nearly 3 years ago it gets a little achey.

Yesterday I competed in a tri/du...one of only TWO women in the oly du. Frustrating to put that kind of work in and have no competition. The woman who won was on a serious TT machine and 3.5mph faster. She's still a somewhat faster runner than I am, but she's also not lugging a spare 20#s. I know that reaching my goal weight would have me at least matching her run speed...but no way will I ever touch her on my road bike (Cannondale SuperSix).

And next year I'm seriously considering a Powerman du (10k-60k-10k). I think that would be a much more enjoyable on an actual aero bike. I'm also thinking I need to consider some local time trials. I'm about to sell my 29er, because the wrist business has made me far too gunshy to go off-road anymore (with the exception of CX).

So, I'm sorta eyeballing this Bianchi. I believe it's about a grand cheaper than a BMC I'm also considering...with very similar components (105). The primary difference appears to be aluminum frame vs. full carbon. Both have the same cheap wheels. For that $1k savings I could eventually upgrade the Bianchi's rims.

I really love the road smoothing ride of my carbon road bike. My previous bike was aluminum with carbon fork and rattled my bones. Granted, we lived with primarily chip-sealed roads at that time. I guess my biggest concern is comfort. Most TT bikes on the market appear to be carbon...would I hate the ride of aluminum, or am I better off spending the same and upgrading wheels? Could upgraded wheels even smooth a potentially harsher ride of alum. and/or make up for any added frame weight..?