The set starting tomorrow isn't what you're talking about here, is it? As far as I can tell those aren't 7x6, and they do have Satan at the beginning, just not MegaSatan.
As to whether Gabe can beat that one... I'm not sure. Depends on if I can kill Satan with Beyzul/Gabriel. I think I can, but I'd have to do some damage testing. And find some friend Gabriels. Hypermax shouldn't matter that much, but I'm not sure if any non-hyper ones exist because I've never really looked. If I can do that I think I'm good. Any other lead and I think I would die on Disco Hera before I could swap Beyzul back out.
That Challenge 10 looks unusually easy though, so I think Ra can do it if Gabriel can't.
No one knew it might be Ch7 until recently, would probably be better if it was, though.
EDIT: It seems that a lot of things in Co-Op got one additional floor if they were originally Legend Plus difficulty and had Catastrophe difficulty added.
All Rogue Dungeons - A floor with 3 PreDras somewhere that all hit 8000 each.
Ultimate God Rush - 10 Million HP Elia as the last floor.
Ultimate Hera Rush - 15 Million HP Zeus&Hera as the last floor.
Ultimate Devil Rush - 28 Million HP Grizal as the last floor.
Ultimate Dragon Rush - 9 Million HP Ilsix as the penultimate boss.
Ultimate Yamato Rush - 18 Million HP Ult Tengu as the last floor. Tengu removed as a possible spawn from wave 1.