I'm currently using a Nikon N80, Ive got a 50mm, a 20-300mm, and a 28mm all AF Nikor glass. Ive also got a SB-80 flash. I have been trying to understand crop factors, and I don't think I'd be very happy with them. Is it worth it to buy a used D100 or D200 from keh.com? Or should i just save up and get a D300 or D700. I currently shoot alot of skateboard and action photography, also concert shots and local open mic acts. What would you guys suggest?