Yeah, a 5D + 35 f/2, 50 f/1.8 and 85 f/1.8 would be just about the size range of equipment I'm looking at. Smaller, actually, but that's as small as it gets on the Canon side!
There's a lot more info on the F-5XB (3 reviews) than the F-8 (none) on cambags.com, and from pics there it looks good. I'm looking for something smaller than the F-6 but primarily thinner (doesn't stick out from your body as much), and from the outer dimensions of 16 x 7.25 x 8.0" (LxWxD) for the F-6 vs. 13 x 5.25 x 8.25" for the F-5XB it looks just about perfect. I also looked at the F-5XC you mentioned, but at 10.75 x 5.5 x 10.75" it's a little bigger like you said, but mostly I don't like the taller form factor as much.
Thanks for the Domke info as always. I've already got 3 of them, and I find myself always coming back to them. Seems like they have the perfect shoulder bag for any equipment combo.