FMJ doesn't actually add damage. It just maintains damage through surfaces.
Lately my friend and I have been running marathon, stopping power, ninja with a silenced UMP. The iron sights on that gun are only rivaled by the SCAR's.
Unfortunately I just did my 2nd prestige last night (really only prestiging until I get a cooler looking prestige icon...lol) so I won't be able to get ninja pro (invisible to heartbeat sensors + silent footsteps) until like level 29. After playing for a couple days with ninja pro my footsteps are so fucking loud to me now without it it's insane.