I do the 3-day split of 'DC'ish' type training...have biceps with back, and triceps with chest/shoulders.
My arms were not genetic freakish, but they used to grow real easy, so I layed off hitting them super hard in order to focus on other weaknesses. I'll say there is nothing like training biceps with a good pump, but i'll be honest, it's my least favorite muscle group to train these days, for awhile now. I can tell right now that my arms are way behind where they should be (i'm 6ft) as i'm cutting down. TBH, I just hate hitting bi's, but I hit them on back day since they are already warmed up somewhat.
I have such jacked up shoulders, it really complicates everything. I swear my arms do not respond as well as they used to prior to shoulder problems. I may take a few months to hit them hard again to see if they respond back where they should be.
Sorry, got off topic with a bit of a rant