Has anyone tried to fit one into a coupe quattro?
Seems like it's not the right dimension for the coupe?

Unless you're running alot of rally races where your batt might get banged aroudn a bit, there's really no use in an Optima.

I think they're great batteries, I ran them all the time in my trail trucks - my 78 Powerwagon for instance, I had to winch about 15 feet uphill on a flooded motor (no alternator). Quite a feat for any battery. Nonetheless, I don't think Optimas are worth it outside of offroad / abuse situations - stick with a stock replacement.