I've been generally quite lucky with TNT - the local drivers know me by name, and I know them by name. Helps that the main driver is an Apple user as well. They've gone out of their way to help me with deliveries, and generally done everything on time. Not always been the case, but for the last few years I've had no issues.
I can wait a few more days (weeks?) without the W5700X, it's just frustrating not having it here as originally stated on the shipping notification from Apple.
From what I can tell, the 580 that's currently in my MacPro will just be sitting on a shelf. I haven't found any particular advice that says having the 580 and the W5700X in at the same time will magically increase performance. Only have one display at the moment anyway.