Whoops, this is an old one. But why open a new one if this topic has been discussed before?
I have a nice pick-up here: (although I cannot be arsed to dig out the SID now, but I'm 100% sure)
Listen to Track 04
of Lotus I (Amiga).
Now scan thru the C64 SID. You will hear the same track, but at roughly 1.5 times the tempo of the Amiga version.