USED Nikon 300mm f/2.8 AF-S I (not AF-S II) vs. NEW Sigma 120-300 f/2.8 HSM? Which lens would you buy if you had roughly 2 grand to burn? Each will probably see TC use. I already have a Simga 1.4x tc that I could use and will probably purchase a 2x. If I were to go Nikon, I'd probably shell out cash for the Nikon 1.7x. I guess we can discuss pros and cons: PROs Nikon - It's Nikon glass? - Sharper TC performance CONs Nikon - It's used - fixed focal length PROs Sigma - Zoom - Price (brand new) CONs Sigma - It's Sigma? - Softer TC performance compared to the Nikon Which would you pick? Help me decide! Need a long tele before xmas for field work!!!