I'd go the 550w if the price isn't an issue. Mainly cuz you'll be in the 300-350w range and the closer to 50% capacity you can run at, the more efficient the PSU is and thus cost less. The 450w can handle that setup, but you're pushing it past peak efficiency to do it. I have the VX550 and its a great unit.
+2. Either can handle it, but I would chose the 550 for the same reasons above.
If you were going to use a PSU calculator I would think the Corsair one would be worth trying. http://www.corsair.com/