I had a GK 800rb rig a while back. With a GK 115 and 210 cabs. It was replaced by the Walkabout/Whappo Jr rig.
TOTALLY different vibe. GK seemed harsh, rude, really strong, even domineering. Tons of tonal variation from the knobs, especially with the bi-amp and crossover freq control, but always this edgy feel. And able to shake the roof off the building or make the tables jump off the floor. Always impressive, but I didn't love it.
The Walkabout/Whappo has all the strength, but a velvety feel and a sense of complete surround, like the bass was going right through your body, and a feeling of warmth. Plus it can shake the roof off the house. True love here.
The Shuttle 6.0 replaced the Walkabout. Very similar vibe to the Walkabout, just more headroom. And now I'm realizing more sensitivity in the higher freq range. Seems like more variability despite fewer knobs. But still the warmth and control as the Walkabout. And it can shake the roof off the neighbors house! Even bigger love!
If you love the GK sound, I'm not sure you will love the GB sound. Not for lack of volume though.