A 460 is FAR better than a 6670. However, it does require 2 6-pin PCI-e power connectors, which your dell probably doesn't have. Dell's tend to come with very low capacity cheap-o power supplies. You should be able to pick up a graphics card that's plenty powerful for less than $200 (the GTX 560 ti can be had for $185 after MIR and is significantly faster than the 460), buy a solid power supply unit (a 650w should be plenty) for around $50-80 and still be under budget. Just make sure to get your psu from a quality company like corsair, xfx, etc.