Westy is probably (no evidence here) doing alot more donkey work and testing more risky and under-developed parts compared to Hopper (who they want to get fast, comfortable and quick ASAP)
Ant has already demonstrated that he has the ability and pace on the bike (QP at Motegi and Sepang last year) .. Plus, testing means sweet 'f' all to be honest, the **** will hit the fan once we arrive at Qatar come round one..