Metal music is actually one of the least demanding musical genres for amps and speakers. It is heavily compressed during recording and mixing and then heavily limited during mastering. Most metal has very little dynamic range which makes it easier to reproduce than jazz or classical.
Assuming that your speakers have a reasonably benign impedance curve you can get away with fewer watts for metal than you would need for other musical styles. However, I think that with 90 dB speakers both of the amps you mentioned are under powered. I would consider something closer to 100 watts so that the amp will be running in its sweet spot when you listen loud.