I'm chiming in on this again, as my standard slab CGFBM just came in. I think it's more comfortable in hand than my FFBM with mags. It may have something to do with the stock thickness combined with the additional weight, but the palm swells of the magged FFBM seem to dig into my hand a bit. I thought it was comfortable until I tried the standards, they seem better. Which one feels better during use remains to be seen, though.
Another thing I've noticed, OT, is that the CGFBM cuts air a lot better than the FFBM. It's a lot handier, lighter and quicker. I'm in love!