Nikon 400mm f/2.8 + 1.4 TC Vs Nikon 600mm f/4 VR

Hi

I'm thinking about getting 400mm f/2.8 VR + 1.4 TC = 560mm f/4 sometime in the next month or two but some of my friend told me that the image quality won't be as good as 600mm f/4 VR. I know the price differ about + - $1000 but it's O.K as long as the image quality produce by it is worth it, I will split the cost with my brother on purchasing this monster so not a big deal but what I'm concerned about is that the image quality between the two. Can someone share some experiences on how these two lenses perform with and without tele converter, how's the image quality of 400mm f/2.8 VR + 1.4 TC Vs 600mm f/4 VR?

Thanks so much