I can tell you my own experience. I've used the TC-17 with my 70-200 VRI on my D300 for a long time and really liked the combo for its versatility. It worked well on the DX body as long as I stopped down to f/6.3 or so. Then I started using the combo on my D800 and I no longer like it. The TC-17 kills the images' contrast. Shooting similar subjects with the TC taken off just underscores how much the image contrast suffers when it's used.
So I too have been considering selling my TC-17. I just don't want to let it go since it may prove useful if I buy some big glass down the road.