One other wrinkle to throw in these upgrade paths that hasn't been mentioned, and this again only applies if you don't mind spending real money as opposed to credits (just like BTuck already did with the Steam Driver bundle) - From time to time WGT will offer you a bundle (similar to the Steam ones) several levels below when you would be eligible from a level standpoint.
In other words, you'll likely be offered a Ping bundle that will include L81 Driver/3WD, L83 Irons (and possibly some Wedges, I didn't do this offer so can't remember) somewhere in mid to upper 70s level.
There was also another one offered to me (which I did take advantage of) around the mid 80s level that included the L90 TM Stealth Driver, L90 TM P790 Irons, and L86/87 TM Milled Grind Wedges. I was very happy with these clubs until I reached the levels where the "best" clubs available come unlocked. In fact if the meter speed was better I would've probably considered sticking with the L90 irons and never upgraded to the L97/100s.
The bad news with these WGT bundles is: 1) you can't purchase with credits you've already earned, you have to get into the pocketbook and spend real dollars 2) you'll get some folks calling you a "cheater" because you will be playing clubs that are above the level they would normally become available (i.e. a L86 player using L90 driver/irons) - just ignore them. 3) these WGT bundle offers only last a limited time, something like 24 hours, so you have to make up your mind quickly and don't really get any time to rent them and "kick the tires" before you buy.
The good news is: 1) you get a great value for what is offered (something like 60-70% off normal price, and they throw in some other things depending on the bundle - coins, credits, balls, etc...) 2) you get earlier access so don't have to grind through the last extra few levels until you can become level-eligible to upgrade 3) unlike the Steam bundles, you CAN sell MOST* of these clubs back when you "outgrow" them to help fund other purchases.
* MOST highlighted because I also did one of these bundles for all 4 of the upper level Titleist wedges, and the only one they won't let me sell back is the 115yd 52* one, which of course is the only one I don't want since it's so close to the set PW.