I shoot Jpg+raw all the time.. But I only use the jpgs for quick filtering.. That is..I find the ones that I want to run thru spp (Sigma's raw sw processor) to create a tiff 16 from the raw as opposed to trying to do,everything in spp at the same time.
W/ the latest fw update and version of sp, when u set monochrom mode on the dp2m, it puts a monochrom flag in the raw file data.. When u open that raw file in spp, it will automatically bring up the b&w dialog. U still have access to the color dialog btw.
I have sep2 as well.. But since the latest set of updates, I tend to use spp monochrome for all the initial b&w work when I create the tiff 16 file.. I feel I can get much better control of the look in my b&w w/ spp then in sep2 (and that is saying something, since sep2 is pretty good w/ the level of controls that u can apply even after playing w/ the different presets)..
I bring it into aperture for my final set of edits.
Jpg+raw is going to be about 50-55mb for each picture and the converted tiff will be around 84mb if u are using large raw. Make sure that u use the fastest sd card.. Writes to sd are slow... 55mb is a lot of data to,write compared to the usually 10-20mb of any other camera.
Good luck and have fun with it..
Gary