I only have experience with the ABM EVO III, but I would recommend checking out the newer IV instead. The EVO III (PRC made) I tried seemed to lack headroom, and had an eq (even with flat engaged) that I could never seem to dial in a mid-rich, cutting tone. The new IV was much better in this regard, but my only complaint was that the fans were quite loud on the model I tested. I don't mind some operational fan noise, but it was just a bit much for my tastes. I would be curious if more current ones have addressed this issue, however. All-in-all, very nice amp- just would prefer one that's quiet. As always, just an opinion, and YMMV. I had to send mine back to the seller, but was within the return policy so just had to pay return shipping. It appears Guitarcenter is once again carrying Ashdown amps, so I may try to demo one again at some point. I had purchased mine with a lower priced EVO Rootmaster 210. Being sealed, and running at 8ohms, the EVO IV could only get so loud. I briefly compared it the an Ampeg V4b RI into an Ampeg 410hlf, and had much better results. The V4B, despite "only" being 100 watts, seemed just as loud as the EVO IV, with a bit of extra tube dimension/warmth. I do think the Ashdown could have had a hair more clean headroom, but not at a volume I'd ever need/use for my gigging situations.
Do I think the EVO IV would be as loud as a GK 1001rb? My gut says probably not, but they each offer their own sonic stamp that many bass players find useful!