Well take a look at this:
3570k (stock) - 77 watts
HD 7850 - 130 watts (for combined 12v rail, 24 amps needed)
2x4gb- 10 watts per module (just an rough guess, could be less)
Fans - Barely use any watts, I would say 5 watts for the average fan.
DVD Drive - 30 watts at most (yours could use less)
Hard drive 15 watts
Just a rough estimation including a bunch of fans and other factors and you come near 250 watts. That leaves 200 watts for overclocking and a bunch of fans. The VP-450 has 2 12v rails of 18 amps per rail. That means 36 amps on both rails is more than enough for the HD 7850 that asks for 24 amps on a single rail.
Edit: Here is a power supply tier listhttp://www.eggxpert.com/forums/thread/323050.aspx
The Antec VP-450 is a very good unit, it's in tier 2b which is pretty good.