The difference between the 4890 and the GTX 260 216 1.7GB edition, is kind of small. The 4890 is better, but not my much. And games that are heavy in physx and TWIMTBP, like Metro 2033, the GTX 260 216 edition will outperform it.
I don't know who told you it would "smash" a GTX 260 216 1.7GB edition, but it shouldn't. It will perform better, but not great deal.
EDIT - Your other computer with the 260 has a lot better CPU too.