I've found that a 174 Champ Orc is the best thumber disc for me, but you already know that's not working for you.
I know a lot of people use Firebirds, and the general consensus seems to be that a more overstable disc works the best. I threw a couple throws with a Speed Demon a while back and that flew pretty nice for me.
As far as weight, I don't really know. I've thrown a few discs (Beast, Orc, XL) in the low to mid 160s, but it was much too fluttery in it's flight with the amount of power I had on it. I've never had problems with a max weight disc for overhands, but I'm also 6'6", 280, and I threw discus and shotput for 6 years so my shoulder is used to having some strain on it.
I'd say maybe try out a few overstable discs in a few different weights (throw other people's discs out on the course, get some DX, or whatever -- with overhands I can tell inside of 5 throws how well it'll work), and then when you find what works for you, buy that in Champ/Z plastic for the inevitable trees that you'll be hitting throwing out of crap.
"a man is a success if he gets up in the morning and he gets to bed at night, and in between he does what he wants to do."
-- bob dylan