ahhh.....don't listen to these "natural limits" people out there, bust your ass, eat some food and you'll put on some muscle, keeping it at 8% is pretty low, I'd love to be at 8%, what are you eating? I'm 5'7 and I weigh about 195 right now, I've been up to 215 and I wasn't "fat"....so you can put on more muscle...not that I'm a giant or anything.
What's your split like?