Bigma or 400 with tele

What would have the better IQ. The Bigma or the Canon EF 400mm f/5.6 L USM Lens with a Tamron 1.4x AF Teleconverter. This would be used to shoot wildlife. I already have the Canon 70-300 IS USM lens. I would guess the 400 by itself would be better but I don't know if 400mm is enough length. I would be using this lens on a 350. Thanks for the imput.

from what ive heard the 400 5.6 with that TC will maintain sharpness equal to or better than the bigma. also, without the TC i can personally attest that it is REALLY sharp, and unbelieveably fast focusing

i would go with Canon EF 400mm. The bigma is VERY heavy.

Whichever you choose, make sure it suits your shooting style. Keep in mind:
400mm+1.4TC = full time manual focus (350D)
vs
50mm-500mm = Auto Focus (HSM smooth & silent AF motor)

I have the bigma and love it but it is heavy.I love the zoom for wildlife but it is heavy.I have thought about the 400mm and then I remember that i need more mm so i have been saving for the real bigma .(aka 300-800 sigma)

I think the prime may be still be a bit sharper.

Actually, the standard Tamron TC will not cause a loss of autofocus on the 400 5.6 because it doesnt report its presence to the camera.

But it'll hunt alot.
I can still AF with my Bigma+my Sigma 1.4TC. It hunts before locking the focus. If you shoot wildlife with it, you can forget about the wildlife.

Ok what do you want sharp detail and light to track birds in flight then the Canon 400mm F5.6. If you want distance and veratile the Bigma.

I own the bigma and will get the Canon 400F5.6 soon only for birds in flight.