I've been shooting Open class for the last two seasons (with a converted sling rifle), and just recently (like last week) decided to jump over to T/R. I'm using a medium palma. But that's mostly because I love my Barnard model P and it's a disgusting fat pig. I also like adjustable butt plates due tot he way I prefer to shoot, so those two factors pretty much force me to go with the lighter barrel. If the weight limit were a little higher, I'd go with a 30"+ heavy palma. I don't see many TR setups with anything heavier than a heavy palma.
I originally wanted to go with a heavy palma in the MasterClass F class stock because I wanted to be able to go back to Open with the same setup (less the barrel, obviously). But it was way too heavy for T/R. Even a medium palma was too much given the action and scope I have (I'm using a Nightforce Competition). So I just decided to keep my existing MasterClass high power prone stock and rebarrel it to .308. Even then, I can't fit in a heavy palma, but only barely. With a lighter action, you could probably manage a heavy palma and the masterclass high power prone stock, especially if you don't care about adjustable butt plates.
The only thing about the high power prone stock for F clas I would change is the angle of the toe, and maybe level/flatten out the fore end so you can shoot it off bags if you want. But even that would add a little weight. Otherwise, it's a great stock, and works well for it's intended purpose (long range sling shooting).
Either way, I'd leave some weight budget to account for inaccurate scales and things like hardware and wood density variations. It would be a terrible shame to have to start cutting up a masterclass stock to make weight, and you don't want to chop the barrel down.
Also, keep in mind that MasterClass isn't known for speedy work. I found I had to send a few polite notes to make sure things kept on track once the original quoted date had passed. Just know that you're dealing with an artist, not a high volume factory. The six months I was quoted wound up being closer to 10. But I'd use them again in a heartbeat. Alex Sitman is a wizard with wood, and went way out of the way to help me out - my rifle was delivered in the peak of the ammunition shortage and he pulled some strings with some buddies of his to help me track down a box of bullets when there were none to be had.
