I'm running a SPAL on both my FBs. They're 16" medium profiles that pull 13A. SPAL is an OEM supplier, so I assume their reliability is good. I'm running an FD alternator on both cars, and haven't had any issues. One of them has 500W worth of audio, so that's around 40A (but those are Class D amps, so I doubt they're pulling anywhere near that amount at normal listening levels).
But really, the fan rarely runs on either car -- only if it sits parked and running or if I'm stuck at a light for a looong time.