Specs and synthetics
We'll start with our customary look at the theoretical throughput of the various cards in some key categories. Keep in mind that, where applicable, the numbers in the table below are derived from the observed clock speeds of the cards we're testing, not the manufacturer's reference clocks or stated specifications.

Although the Radeon HD 4890 OC and GeForce GTX 275 are ostensibly direct competitors, they diverge from each other quite a bit on paper: the GeForce easily leads in fill rate and texture filtering capacity, while the Radeon has a clear advantage in shader FLOPS. Despite different memory types and interface widths, though, memory bandwidth is roughly equal, with a slight edge to the GTX 275.

Incidentally, the GTX 275's place in Nvidia's lineup is probably worth calling out. Notice that the older GeForce GTX 280, based on the 65nm GT200 chip, trails the 275 in texture filtering and shader arithmetic capacity. So although 280 is a higher number than 275, the newer card may prove to be superior in many cases.

This would be an unexpected result, were it not for the fact that we've seen it many times before. In spite of the theoretical numbers, the Radeon measures out with more real-world pixel and texture fill rate.

And despite the 4890 OC's pronounced FLOPS advantage on paper, the GTX 275 leads the Radeon in two of the four shader tests.