Discraft Z Xtreme. However, I have a heavy Flick that sat outside for 2 years and got a bit warped. It may be the single most overstable disc in the world. And then there were the prototype Wildcats Discraft made with a special stamp for a3disc for the first One Disc Challenge. It was funny watching guys make throw after throw that went into the woods on the left from the practice tee at Hudson Mills out onto (intended anyway) the practice field.
Funniest thing EVER, Groove is not Understable, frickin meathook driver, biggest lie i ever heard, -2 on Turn, lmao, bahahahhha! That or the Whippet has to be the most Overstable. My force is a close 3rd.
The most overstable disc I've ever thrown was a white, super flat 150 ESP Flick. Whether I threw it forehand or backhand with anny...it always finished in the pattern of a Halibut hook and would be traveling at the ground almost vertical.
How many people know what a halibut hook is...great Alaskan fishing reference there. I'd like to see you throw an Xtreme, only disc I ever gave up on after throw. You could probably handle it a bit better than I could.