At 5'9" a 52cm may even be appropriate for some people.
Just because I recently went through tri bike shopping(not that I wanted to, someone stole my old bike) I thought I might add some thoughts up here.
Trek - Trek overhauled their line up for 2011. They now have three "lines" the 2 series of aluminum, the 7 series of carbon but with a standard front end and a 9 series with an integrated fork and front brake. I ended up buying a Speed Concept 9.5 so I thought I'd throw some thoughts out here. The bike looks ridiculously aerodynamic, the tubes measure 28X80mm in most places, the headtube is under 30mm thick at the narrowest point, the integrated handlebars are also very thin and the fork looks clean.
Trek's biggest selling point to me was the good fit, integrated accessories and flexibility of the bike for longer course racing. There is 2 bottle mounts in the frame, and even one possible one on the top tube that would probably accept an aero bottle and not interfere with a person's knees. There are Bontrager aero bottles, a more integrated "bento box" and a "draft box" which functions as a more aerodynamic seatpack for carrying a spare tube.
The bike fits very "midde ground". It's not as long and low as Cervelo's P3/4 and it's not as tall as Blue's Triad. It's middle of the ground. The 9 series comes stock with a 60/45 stem. You can also get a shorter 50/10 stem or a longer 100/45 stem or a long and low 100/10. There is more stem sizes but honestly, you should probably buy a different bike if you are looking for that much height. The stock stem allows me on a size small to get 12.5cm of drop with a 71.5cm saddle height. I normally ride with 14cm of drop but am hesitant to go with the 50/10 stem.
The frameset felt lighter than my old Felt B2 setup but I didn't get a weight on it.
So far the bike is fairly amazing to me. I've setup the brakes myself. The front brake is actually fairly impressive in setup and function, I really like it. The rear is more of the difficulty you would expect from a something thats completely hidden from sight. The function on the bike is good on both, I haven't thought about them yet which is a good thing.
Because I was helped out by a shop, I got a pre order model but I would stongly recommend Project One if you are interested in the speed concept. It costs like $10 extra and a few extra weeks but you could actually get a $5150 rival equipped Speed Concept and get the color of your choice.
Nitpicks would be that the basebar grip on the bike has an upturned part that to me is unnecessary. They should have left that off and the length and basebar would have been perfect to me. Oh well. Second would be that there is no micro adjust on the rear brake, so if your cable stretches after install, then you need to open the rear cover and re-tighten the brake manually which is a pretty big pain from my perspective. I'm looking to get a brake lever which would offer a small amount of adjustment.