I used a 400-RB with an SWR S-15C for 8 years. I recently switched to an SWR 350, simply because I wanted a little more headroom. The S-15C (like the S-15D) is an 8 ohm cabinet, so the 400RB only drove the speaker with 120 watts. That meant in situations where I had to play loudly, I maxed myself out pretty quickly. Still, it gave me great control over my tone. With the SWR, I'm still only getting 220 wats going into the speaker -- but that's 100 watts more than I had. One other thing to consider about the GK -- it's completely solid state, so it (to me) has a slightly less warm tone than tube or tube-preamp systems.