Hi Rooz,
I too have the R1C1 and use it with a Sigma 150 2.8. A pretty good combination. The light is just so nice and even in macro shots. The flash units are low powered compared to the SB800 and they are really designed to give soft even light to your macro target which would typically be less than 1 metre away. When I'm doing portraits, I use twin SB800s for the extra power because your subject is typically a few metres away.
The SU800 (part of the R1C1 kit) can trigger any of the
modern Nikon flashes remotely, SB800, 600 etc.
The only small downside is that the flashes and the SU800 commander run from CR123A batteries. These are quite expensive compared to
AAs and as they are such a small battery, you'll only get 40 or so flashes from a rechargable before you need to recharge it again. For that reason I have 2 sets (6 rechargeable CR123A batteries) and a SB800 as backup
You'd probably find the capacity of the non rechargeable variety better, but it would work out darn expensive.
The light is unbelieveably even and if you really want to you can add extra flash units up to a max of 4 in a ring around the front of your lens, but I find the light from 2 just so nice I don't think I would ever bother adding more flashes.
Hope this helps.
Cheers
John