Your GPU and CPU are the same link.
That is OK. If you absolutely want nVidia, go with that setup.
I would go P45, 4870 right now (better bang for the buck), but it's up to you. I don't have any complaints about my 780i, but I think you'd get a better value with the other mobo/GPU.
That case will not cool that well. Look for a better cooling case.