Originally posted by Adam
I've found that you get much better results around 300 F2.8 and without the teleconverter, just blowing the images up. Not bad shots, though!
100% agree with Adam on this, I just don't have a 300 F2.8

but its on my wish list. But using my 400mm with a 2xTC vs the same 400mm without the TC and just cropping, I get a lot sharper image without the TC. I normally start shooting at 100 ISO and shutter around the 1/160 mark and then play with the settings from there.
With the focusing, you should be able to just set the lens to infinity and not touch it.