Have you guys used this
size calculator over at the hypertrophy-specific board? Pretty useful to waste some time at your desk job at least...
Supposedly it can use your wrist, ankle, and height measurements in inches to predict how big you can get naturally at 8%.

Definately isn't 100%, but it's a good motivational tool.
If you don't have a tape measurer, just
click here and print one out.
I measured 8.0 wrist, 10.8 ankle, and I'm 69.5 inches tall (I also have blue eyes and a rapist's wit

)
Told me I could get to be 228 lbs, 52.6" chest, 18.1" arms, and 28.3" thighs. My arms certainly are bigger than "predicted", but at 8% bodyfat it may be correct afterall! I'm bigger now, but I'm double the bodyfat, so who knows.
One of the flaws I can see with it is the ankle measurements. I know from the military that sprinters have really tiny ankles whereas long distance runners have really thick ankles. Be that as it may, enjoy!