Usually, you want to set the gain to be high enough not to go into clipping, then adjust your overall signal level with the Volume control. Same method for both your combos.
On the Rumble, the 3 pushbuttons to the right of the Gain knob are for preset EQs, "Bright", "Contour" and "Vintage". The manual indicates that there is some interaction between Gain settings and the Vintage and Overdrive features. Here's the manual:
https://www.fmicassets.com/Damroot/Original/10001/OM_Rumble_40_100_200_500_US_5.pdf
The combos use very different EQ circuits, so setting one the same as the other doesn't really add up. You need to get a setting you like on one, then set the second EQ to match, using your ears and not your eyes. What I see is that you favor an EQ that's really heavy on the treble, light on the bass, and scooping out all the mids. While each of us has our own idea of our ideal tone, your setting seems a bit extreme. Why the aversion to mids?
I think you've done some good research and have come to some useful conclusions. If you like the clean sound of the Rumble more and it's not enough power, there is either the Rumble 210 combo or a Rumble head and cabinets.
I got the manual with the rumble (what's the odds ha ha) and it was pretty straight forward. I didn't turn the gain/ overdrive function on but I did have the Vintage button pressed (I think) also have the GK manual haven't read that in awhile. I find it interesting or maybe annoying the GK has no sound if the gain knob is fully counter clock wise. These aren't my preferred settings I don't have any yet, it's just me trying to get the best sound and most volume out of each Amp. I turned the bass up until it clipped and then dialed back. It's true I did the same to both. At this point I don't have an aversion to mids (pics say otherwise) it's just where I ended up. I think the gain on the GK was turned up because that along with boost and Master volume just kept giving me more volume. I honestly don't think the GK is capable of a clean sound. I do like to keep things as simple as possible, but when it comes to these low frequencies and amps it seems nothing is clear cut. Thanks for the suggestions I'll Def try them out !!!