No, it had to be Game 7 in '89 or '04.
In '89, first Smyl misses the damned net. Then Otto kicks in the Game winner. I've always felt the '89 Flames should have their names sanded off the cup and replaced with the inscription "1989 - A Bunch of Fricken Cheaters."
In '04, there's the incredible high of Cookie scoring to tie it in the last seconds. Then the deflation of the power play goal within seconds of the start of overtime.
Now, the toughest Game for a Flames fan to have watched would have been in '94 when Captain Kirk made "The save".
Modo vincis, modo vinceris.