Thanks for the info, guys. Bikesdirect didn't have any 52s on their popdown menu for the Nemesis with DA, but I've emailed to double check. I'm going to go for it if they have one. If they only have 54s, I'll have to actually ride a 54 frame first to confirm it would fit. I have a 55 Lemond - more of a road bike geometry, and it is too big for me with tri bars.
It does sound a little small, and I bet the top tube is shorter than the 52 frame. I'd say check a similar bike out in a shop before you commit to buying the 49
I know you are looking at tri bikes, but I just wanted to give some feedback regarding the Motobecane brand.
I have the Motobecane Le Champion and it is fantastic. I've had it for about 10 months and put a fair number of miles on it during that time. It is a fabulous bike and only cost about 1/3 of what the bike stores would charge. I recently took it in for a tune up (annual, didn't even need it) and the staff was drooling over it.
Great components, solid build, unbeatable price. I wouldn't hesitate to buy another.