The Open is 4 rounds and I think the WGT is set for 2 rounds so you have to take that into account. St Andrews is one of the more tame Open courses and without rain or wind there is no real way to protect par, there however if rain and wind comes then the scores will go up. A more fair bet would be the US Open but obviously we are playing at a different course than are the men. Back to the Open, I think that the final two round score will be under par but not sure how much. Is your intent to take the winner's final two round scores to compare to the WGT winners score?