Alright. I have a 7800GT myself and I have an Antec 2.0 550W PSU. Contrary to popular belief the 7800 doesn't use that much power. Nothing like 250W, nothing uses that much power. If you have a solid and stable PSU I think the 460 would do you good. 600+ Watts seems to be going overboard.
I'm not familiar with Enermax so I don't know how stable and efficient they are, but that's my two cents.