If you want to save money, it's fine. It's just that the modular PSUs will allow you to remove unwanted cables, that's all. I think that if you will downgrade some unnecessarily expensive parts such as the ones described below, you might find enough $$ for a modular PSU.
Anyway, both your mobo and GPU are overkill... I'd get a P8P67 Pro or a P8Z68-V Pro (a better choice since you have an SSD), as I said, and Crossfire 6950s/SLI 560 Ti's, that's enough to shred any game nowadays @ 1080p. But if you have a lot of money, by all means, get a 580 or a 6970 and SLI/CF later...
Case: check out NZXT Phantom, costs a bit less, yet great cooling and looks better than any HAF cases.