man being a hard gainer sucks! the more you work out, the easier it is to kinda grow out of it. i'm 6'4 about 195-200. when i graduated in 06 i was about 160 (thats skinny as **** in case you didn't know). all i did was eat about 6 meals aday, used muscle cytogainer for awhile then switched back to muscle milk, plus working out for 2-3 hours 5 days a week.
as far as no2 goes, i never liked it because it makes the muscles in my arms pump too much, i could only get about 2 sets of 10 in before they are swollen so much i couldn't get full reps in. makes you look bigger for a bit though!