Yeah, but surely if it isn't 'branded' Duck tape then it's duct tape.
Anyway, having a speedup on games that were designed for the C64 will just make 'em unplayable, as anyone thats tried playing a game for an early Amiga on a later one can testify ;-)
Some games were, however, done on both C64 and Amiga, with the Amiga version being identical apart from having more colours and better sound (sometimes smoother too).