Another one of my local residents looking for work... D300 Tamron 18-270 F5.6 @1/1000 -.33EV PP in OneOne 7 and CS6 I know that this sounds crazy - I need a lens with a faster AF Dont know what to get I have the 80-400VC Tamron 18-270 as my work horses....
Would that be a lot better than the 80-400 at the 400mm x1.5 crop factor = 600mm at 6.3. Does it focus appreciable faster. I hear it still hunts !!! I get good results with the room It's got to be better with the prime
If you have to stay in that price range the 300/f4 + TC is probably your best choice.
If you can swing it, the Sigma 120-300/f2.8 (either older DG or the new DG OS) would be a truly significant move up in both image quality and focus speed from the 80-400. With a Sigma 1.4TC you get 170-420mm at f4 (with the DX crop factor, your D300, that is 255-630mm equivalent.) You would be surprised at how much it helps, both focus and shutter speed, to have an f/4 lens at 400mm.
Sorry for not getting back sooner. That combo you just ordered is significantly faster than the 80-400mm IMO and even with the 1.7tc will usually out focus the 80-400 IMO.(that is with Nikon tcs,I don't know about off brands). No VR is the only downside that I can think of but it has pushed me to use my tripod more often.