The "Straight" Disc?

A lot of players, myself included, seem to search for a mythical straight flying disc. There are some discs I have that sort of fly like this a Z Buzzz and a beat Electron Envy. However, above 5 speed this seems elusive. Has anyone else just given up on finding a straight flying disc? How much fade or turn do you find acceptable enough to be "straight"? Strongly considering just playing a turn disc and a fade disc in each slot.