p.2 #1 · Sigma 50-500 OS vs Nikon AF-S 300 f4 + tc14?
I haven`t had much time to test my 300 f4 but shot some pics of the kid in the snow last weekend.
This lens really performs With my D700 and AF tracks really fast and accurate
Saving up for a D7k and a TC14EII for more reach now.
p.2 #5 · Sigma 50-500 OS vs Nikon AF-S 300 f4 + tc14?
If you get a good copy, the Sigma can produce excellent images. However the Nikon, as noted above, is simply better in all respects. It also works extremely well with the TC 17 as long as you use proper technique. This boosts it's top end to 510mm. I have it and a 300 f2.8 VR and the IQ isn't really much, if any, better than the f4.
p.2 #6 · Sigma 50-500 OS vs Nikon AF-S 300 f4 + tc14?
you made the best choice, i chose the 300 f4 af-s and tc 14ii over the sigma for its pseudo macro capabilities shooting butterflies and dragonflies.
reading about the sigma i found it to be less sharp over 400mm. very light hungry (f6.3 over 200mm), bigger, heavier, more prone to qc issues, plus its effective focal length drops off rapidly if you get closer to the subject.
the nikon doubles up as a great, sharp, birding/bugging lens.
I manage fine w/o out it 
