I had the same idea and went ahead and built a Trek TT. I too have a 5200. Honestly, the TT has a lot more lateral stiffness and less flex in the bottom bracket area. I am planning on using the TT to do IMWi in 2005, but 2 half ironmans this year. Hope this helps.
If you sit shallow, have a long femur and a long torso this bike may be a viable choice. I sure wouldn’t want to run a marathon after 5.5 hours on a shallow seat angle bike. I’ve done it. Ouch.