I love brainstorming army ideas! Especially at lower point totals, since it tightens up the wiggle room on making sure your army is effective.
I really like the Grut armies posted. I'm no expert on Arrow Grut armies, but I think I would probably take the Raelin variant over the Mimring one, personally. Mostly I just like the security of the extra Arrow Gruts, which probably stems from me not being super comfortable with Arrow Gruts in a high-level setting. I'd be all for that Blade Grut build, though. A Heavy build would be interesting too, maybe something like:
Heavy Gruts x2
Nerak
Grimnak
Syvarris
Or maybe switch out Grimnak and Syvarris for Tornak and Kaemon Awa, or maybe even Ornak and a Fen Hydra. Notice, though, that I'm more likely to play low numbers of Heavy Gruts in an army because I'm more comfortable with them.
I do think that Nilf/10th is too strong for RtW, and would never want to give that army to my opponent. Cool that it comes out straight to 410, though.
Probably worth tossing out an army that came to me. I call it "GenCon's Favorite Things" because I see these guys praised all the time in a lot of GenCon relevant threads (and I find it interesting that a lot of good RtW units came from the DnD waves):
Eltahale
Phantom Knights x2
Mezzodemon Warmongers x2
I'll be brainstorming more ideas too, I'm sure. I really like coming up with RtW armies.