OK, so I am going to buy myself a second head - primarily for backup purposes. I currently run a redface SWR Bass 350 (pre-fender, if that matters) and I REALLY like the tone. I was thinking about getting a second Bass 350 so I have a consistent tone with both heads, but at a couple of recent shows I wished that I had a little more power. There are lots of other SWR options that would give me a bit more power, but since I'll likely be looking used I likely won't have a way to compare tone. How different do the heads in the SWR line sound? My front runners are the SM-400 500 or 900, the 550x or 750x, the 750 (not X) or another Bass 350. What are everyone's thoughts? Thanks!