The GTX 420 is really a big step down from GTX 460.

This site doesn't have an actual benchmark of the two cards, but it shows you some of the important performance statistics

http://www.hwcompare.com/8233/geforc...e-gtx-460-1gb/

As you can see, some specifications are similar, such as the clock speed and memory speed. However, the memory bus width is twice as big on the 460, and there are more texture and render units.

You can imagine this as a road infrastructure in real life. You have two networks of roads, both have a speed limit of 60 mph, but one of the road networks has twice as many lanes than the other. In addition, one of the networks also supports trucks with twice as much cargo loaded in them.

Furthermore, when these trucks get to their destination, you can imagine them reaching a manufacturing plant. Both of the plants work at the same speed, but one of the cards has 4 times as many manufacturing plants as the other does.