I ride a Cervelo P3 size 48 and love it (but it does have 650c wheels). Have you looked into Aegis? (My next bike currently on order pending my paint color.......) Custom paint job, carbon frames, hot bikes! I know for their Zaero frame, they make 2 small frame sizes for whichever wheel size you want - 650 or 700 (I'm going with the 700s since I can this time). Not sure about their geometries for T2 or Trident (their other 2 tri frames). Call them up - talk to Greg or Pete and they'll help you with any questions you have. Here's the website:
www.aegisbicycles.com

Good luck!