I had a Black Dog (bridge) in a V, so pretty similar to an SG.... all-mahogany anyway. It sounded fine, not muddy at all, but it is relatively dark compared to the Riff Raff.
The neck pickup was an AII Stormy Monday, which felt a bit "light" next to the BD - not enough contrast between the two pickups (IMO, of course). Next time I'd go for a neck pickup with a little more oomph and midrange - an AIV Mule probably.
I think the Riff Raff bridge is nearly perfect in an SG, but it is bright, so I'd want something warm in the neck for contrast. I haven't tried the RR neck, but I think it'd be too bright for my taste. When I eventually change the pickups in my Tokai SG I'll probably go Riff Raff/Mule or maybe an AV/AIV Mule set.