The SWR Super Redhead paired with a Goliath II 4x10 8 ohm was my main rig for many years of road work with a VERY loud band. The Redhead was rock solid and always sounded good, but I must admit that it isn't the ideal rig for hard rock/metal. First of all, it is a very "pretty" and neutral sounding amp: sort of like a warm and loud direct box. This is not an amp that has "nuts".
The trick to getting it to cut with a rock band is to 1. Put a good compressor in front of it to knock down the transients a bit 2. boost the mids to taste and 3. Turn the Aural Enhancer knob to about 2 o'clock. Although the Redhead has plenty of power to get the job done, it does run out of headroom when you really dig into it. In a hard rock/metal band, that's, like...um, every note! So I know where you are coming from.
Stock, the internal speakers are 4ohm. I ran it at 2.6ohms for years and did not have any trouble with the amp. I did, however, go through the stock PAS drivers more than I would have liked (about 3 pairs). I also noticed that running an 8 ohm 4x10 with it caused the amp to push more power through the amp's speakers than the extension (which you would expect), causing an unbalanced sound.
On the advice of SWR, I ended up replacing the 4-ohm load PAS drivers with Eminence Neos running 8 ohms. Not only did the extended x-max of the new drivers extend the low end, but the amp was substantially lighter. Also, the amp wasn't working so hard and the sound was more balanced. Definitely an upgrade.
If you are shopping for a new rig for a rock band, I can give you a tip that worked for me: Mesa M-Pulse 600, Avatar 410 8 ohm, Avatar 2x12 8 ohm. Dialed correctly, the Mesa sounds like the Redhead and an SVT had a Baxandall love child. I couldn't be happier with mine.
Good luck.