Hi - I don't think I've posted before, but thought I'd chip in here as I've (very nearly) the two amps and listen to quite a bit of metal.
I've three integrated amps: Accuphase E-550, Leben CS600X and Mcintosh 6700 which are rotated between Peak Consult Princess V and Kudos Titan 606 speakers. If I were to pick solely for listening to metal I'd put the Leben and Mcintosh joint second (Leben for normal levels, Mc for louder in big rooms) but the Accuphase quite far ahead of both.
The Accuphase can be beautifully visceral with great texture (lead guitrs) and I've never found it wanting in the drive department.
My comment about the Mcintosh is possibly more to do with their house sound (music tends to pleasantly waft over you vs make your ears bleed) rather than the pros/cons of more watts.