Checking Newegg, you're kind of out of luck with GTX 680's at $450. If you really wanted to go that way, you can get the MSI GTX 680 Twin Frozr or Gigabyte Windforce for $440-$450 after rebates.
But really, you can shoot the moon at that price range and go for the very best GTX 670 without losing out on any noticeable performance. Again looking at Newegg, the top choices are going to be:
- MSI PE/OC for $380
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
- Asus DirectCU OC for $410 after rebate
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
- EVGA Signature 2 FTW+ for $420
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
- Galaxy GC for $380 after rebate
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
- Gigabyte OC for $380 after rebate
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
If I were picking from that list, I would go for the MSI Power Edition OC with the Twin Frozr IV cooler. The Asus would be a consideration, but it's too expensive. In terms of performance, the MSI Twin Frozr IV cooler will maintain the lowest temperatures, which in turn will enable higher, more consistently maintained Turbo Boosts for overall higher performance. It comes with all custom "Military Grade" components, a high factory overclock, and quiet fans that spin backward for a few seconds at boot to clean out the dust. How cool is that?
http://www.hardwarecanucks.com/forum/hardware-canucks-r...
http://www.guru3d.com/articles-pages/msi-geforce-gtx-67...
http://www.techpowerup.com/reviews/MSI/GTX_670_Power_Ed...