In regards to TT frame sizing.

All my road bikes are in the 56 - 57cm frame size.

Even my bike set up for TT's (IM's) was until recently on a 56cm road frame. Just with the seat as far forward on the rails and the aerobars (Vision Tech integrated) as low as possible. This worked adequately without impacting the handling characteristics of the bike too greatly.

Limitations of the road bike frame is the top tube length and length of the steerer tube. So even with the seat forward, it is difficult to get the upper torso as close to horizontal as possible.

The benefit of the steeper seat tube and shorter steerer tube is to allow the hip angle to stay as 'open' as possible and get lower at the front (imagine rotating your position up and forward around the bottom bracket).

To put this all into perspective, I have just recently bought a 52cm P3 frameset. Although the frame is considerably smaller than my roadbikes, the fit is amazing (due to the extreme downsizing the front end is a little twitchy) which I am willing to manage for the aero benefit. I was very sceptical about such a significant downsize, but a triathlete friend of mine who is nearly the identical size let me ride his 52cm P3 and I was sold on this sizing immediately!

In regards to crank length, go longer rather than shorter. The additional leverage of the longer cranks should allow for greater wattage.

Check what rules the TT series you are looking at race under, as if UCI the saddle nose must be 5cm behind the bottom bracket. Steeper seat tube angles will most probably put you well forward of that - so a stumpy nose TT saddle may be required to get around that ruling or a more moderate seat position.

Try the slowtwitch.com forum (taking most with a grain of salt like any forum) plus also check out some of the tech fit articles at http://bikesportmichigan.com/wheels/wheels.shtml