i've done a fair bit of hunting around and have decided that both lens are great for their price. both have an equal amount of pro's and con's.
my question is...would you choose the 80-400 over the 150-500 for the same price.
for second hand lens they come in at about the same price, and i simply cant decide if i want to go with the nikon lens or the sigma.
the type of shooting they would be used for is nature, aircraft or the like.

ideally i would like to hear from someone who has had both, or someone who has used a lens that stops at 400 and then also used or owned a lens that stops at 500, and can tell me how much you notice or look for that extra 100mm.

the lens will be used on a d90.