I had a custom stamped firebird (so I don't know if it was a 12x or what) that was flat topped and was very overstable but it somehow has disappeared from my bag. It was perfect for short to medium range flex shots. All the regular 12x firebirds I've thrown are much less overstable and are not what I'm looking for. A friend let me borrow his old champion style plastic Pro firebird and it was very similar. My question is what disc will fly most similar to those "good" Firebirds?