my fave thumber disc is champion starfire.. throw it at 11oclock, cock your wrist at 1 or 2 oclock, throw it like you're in center field throwing to home plate... highly accurate once you get the hang of it..
also like the 150 tbird for distance thumbers.... same glide pattern, i can just heave it a little farther...
Texas players are very fond of their overhand discs, and there are two that outsell all others in our Superstore: The Discraft Flick and the Aerobie Epic. The Flick is super-overstable with a low-profile so it slices through the wind and behaves predicably for overhand shots. The Epic has an eliptical rim, making it easy for just about everyone to grip. It can also be tuned (by bending it up or down) to adjust the flight. I'd estimate that these two discs outsell all others combined with our overhand customers by a large factor.
I'd recommend going with a lighter weight (i.e. 160's) to save the wear-and-tear on your shoulder. And, as others have mentioned, any very over-stable driver will work fine if you don't care for the Flick or Epic.
i suck at overhand/tomahawk, but one of my buddies throws star or champ boss for every drive (which are always overhand) and when the holes are long enough he's 400+. this is in boulder though. a bit lighter air. it gets windy though and he carries a star xcal for those situations. somehow a couple of my friends (one the aforementioned and the other is one who throws overhand occasionaly) are able to turn both discs over so they either land upside down or on the rim for a beautiful straight skip/bounce which equates to an extra 20+ feet... consistently
I use a monster or max. Whatever disc you decide to go with, just be sure to over do your follow through... Like step back and really make sure your arm keeps moving and you step forward and touch the ground in front of you. The overhead shot can tear you up so fast! I love it and use it well, and that my friend will add accuracy and save your shoulder..
I see alot of people going overstable. Throwing the tomahawk/hammer is like throwing a baseball down hill. Try a Valk first off say in the middle of the end zone of a football field aiming to land in between the hashes. Once you get some more snap (the last 10%) try moving to an Orc or Wraith. The more stable the disc the longer it will take to roll all the way over. For a thumbers THE PRO uses sweet CE Firebirds.
+1 for the 150g Z-Flick. Personally, I get a lot more "D" with lighter ones as opposed to heavier ones. I feel that it is a function of arm speed and for me, that means lighter weights.
Another disc option I have discovered might surprise a lot of people; a 150g QOLF! I'm getting great distance and accuracy throwing thumbers with these, and that is even with a bit more left-to-right action than Flicks.
Here's a weird thought for you. My favorite thumber disc is a Comet. If I ever need to lay up, or need to be 200 feet straight in front of me with no skip, bounce or left right movement, my comet will do just that.