Anyone using the 300mm f/4 AF-S + 1.7x teleconverter on a d7000? Opinions?

I'm looking for opinions or sample images of the 300mm f/4 AF-S with a 1.7x TC on a d7000 or comparable DX body.

I'm upgrading from an old sigma 70-300($130 version) to the 300mm f/4 and I'm trying to gauge whether the 1.7x TC will lose too much detail for the combination(300mm f/4 + 1.7x) or if I should just get the 1.4x TC instead.

I really just want more reach for birding with as good of quality I can get. I'm in the desert with pretty good lighting most of the time.

Thanks for any input.