What I first noticed was how punchy and articulate the ACB was. The speaker plays a part in that I think. A fat but "focused" sound (thank you mids), very responsive and touch sensitive, and something hard to explain but the transients pop nicely while the sound which comes after sort of settles if that makes sense. So a mix of tone, articulation and response. It makes the flats sound even nicer. I've not been able to get any break up yet, stuff was rattling around in the house too much as I pushed the volume.
So going back to both my Rumbles, they still sound great, but if I use the vintage button to thicken the sound it also muddies it a bit. I tend to leave it off, but that's also a compromise and there's no way of adding a hint of OD because the inbuilt option is not subtle and thins out the bottom end. You can EQ for that, but then it's not footswitchable to the other setting without redoing the EQ. The Rumbles sounded great with the JHS Punchline, but that bypasses the preamp and tone controls.
So in short, I like the Rumbles a lot, and they outperform their price point, but they have some compromises. They're certainly a lot lighter....
The sound I'm chasing in my head is Jerry Jemmott or an early 70s rock bass with some break up. Spotify says my listening age is 69...