I'm in the process of finalizing my parts list and read about how important the power supply is. I wanted to run my build by you folks to check if my power supply is sufficient for my build. I used the psu calculator, which told me i needed 350w (which i felt was suspiciously low), and i opted for a 500w psu to be safe. Should i get one with higher wattage or am i good to go?
500 Watts is PLENTY. Heck you would be fine with 400W if you weren't planning on doing any major upgrades and didn't mind using a molex to PCI-e power adapter... This is even more the case since you went with an i3 as opposed to an i5.
As stated 500W is plenty, and you've gone for a decent brand. 400W would power it, but probably not at the same level of efficiency.
I've tested systems similar to the OP's, but with a GTX570 ( ~80w higher draw than a 6870 ), ~320w from the wall running Furmark / ~85% efficiency ( TPN550 ) / ~270w load on the psu
As far as efficiency, the OP would be closer to that magic 50% load figure with a 400w psu ( When running a power virus )