Are you really going to train on tubulars? IMO, if you go for carbon fiber rims it makes little sense aerodynamically to go shallower than 50-60mm. With 38mm rims you don't save enough watts over the best aluminum rims IMO. Check out the November Bicycle blog and wind tunnel tests and realize not all carbon rims are created equal. If these cheap chinese rims make sure you're getting wide "U" shaped rims.