I can tell you now that without upgrading your PSU, your probably not going to be able to get any better. Actually, without upgrading it, I'd be cautious with getting the 460 in the first place. The thing that people don't take into consideration is that your not just looking at the max power your PSU puts out, as this is distributed among several different lines or "rails". For example, your CPU uses a 3.3v rail of your PSU to get it's power, whereas your DVD drive, HDD, and GPU use the 12v rail.
What does all this mean? It means that you could be looking at a card calling for a 450W PSU, with a recommended 24 amp 12v rail, where you've got a 460W PSU with a 15 amp rail. In my example, you PSU meets the maximum power recommendation for the card, but the 12v rail doesn't.
I've been trying to figure out how big the 12v rail(s) on your PSU are with no success. You could probably take it out of the case and it will be on a label somewhere on it, but I dunno if you want to do that or not, but if you did and it was on there, that would be a big help.
Here's a good read if you get bored:
Power Supplies Explained.