I use a 5x4 in my dorm room, which works just fine even though I'm running at 1680x1050. At home, I use a 9x12, which has more pressure sensitivity and is slightly more accurate, and also works much nicer for broad strokes.
I'm not sure what you gits use A5 and A6 for- do you just not like specifying precise measurements?
I'm not sure what you gits use A5 and A6 for- do you just not like specifying precise measurements?