That seems like a quite inefficient system: It's set up badly for each gun you use :S
P90 mags on your front, meaning you can't crouch without snorting P90 mags, and M4 mag pouches in the small of your back... and only pistol mag, no dumper for your M4 mags ( which would be insanely hard to put back into mag pouches in the small of your back surely?)
Specialise, don't generalise!