I just got to Master and i have to say its a big jump in difficulty...
Oh, wait until you get to Legend to say that. LOL
As rules of thumb in general, you'll need clubs of high trajectory as you move up, facing faster greens which in other workds, you'll be dealing with hard concrete-like surfaces so if you want your ball to get real close to the pin, you definitely gotta go for higher trajectory + more backspin on your clubs (and more backspin on your ball as well).
WGT introduces new clubs and balls in the pro shop quite regularly (and it's been a while that I haven't purchased any additional clubs as I've got them all maxed) so rather than pinpointing which club to purchase, it'd be better to say any club that achieves the above is good one for you.
Good luck in your journey of WGT mastering.
P.S.: I just checked you profile and... you must've been taking helluva break since you joined in 2008!! You must be one of the very first members of this game! Welcome back.