Groupset: The 10-3 comes with Ultegra, the 10-5 comes with 105. Ultegra's higher up the Shimano hierarchy.
Components: The 10-3 come with the C2 version of their stem and seatpost (more carbon, lighter). The 10-5 comes with the C3 version (carbon-wrapped alu).
Wheelset: The 10-3 comes with Mavic Aksium, the 10-5 with Shimano RS-10. The Aksium's a better wheel IMO.

I'd go with the 10-3 if both are priced the same - more value for your money.