My bf is about 13% measured with the bio electrical impedence thingy (Omron BF302). And I'm about 155lbs, 5'9'' (177cm)
In the winter I eat as much as I feel like, and allow some cheating to up the kcals. Around february I start eating really clean, but I don't diet like most people here, e.g. counting kcals and so on. I just make sure to get lots of protein, lots of low GI karbs and as little fat as possible (plus essential fatty acids supplemented).
I think i've overtrained by bi's for years. These days I just do a few sets of biceps curling in the chins rack (i.e. underhand grip glose grip pullups) and one or two sets of hammer curls following every back w/o and they grow quite nicely (albeit very slowly). I dont have an "arm day" any more.
I do forearm work as well, no straps deadlifts, gripper work and curls. I've always wondered if you can grow bigger wrists doing forearm work, anyone have any info on this?