The theory—and practice
To see how the changes to the GeForce GTX 260 affect its position in the grand scheme, here's a comparison of some recent graphics cards. Note that we've derived these numbers from the actual clock speeds of the cards we're testing rather than from the stock clock speeds established by the GPU vendors.

Like I said before, the GTX 260 Reloaded comes very, very close to the original GeForce GTX 280. By contrast, the Radeon HD 4870's theoretical throughput is unchanged by the addition of more RAM.

In theory, it would seem that the GTX 260 Reloaded should have the edge in fill rate and texturing capacity, while the 4870 1GB ought to have more shader power. However, these things are often complicated in actual use by the quirks and varying efficiencies of the GPU architectures in question. Here's how things shake out when we measure them with 3DMark's directed benchmark tests.

This is pretty much the inverse of what we expected: the 4870 1GB proves faster in the color and texture fill rate tests, while the GTX 260 Reloaded takes three out of the four shader processing tests. Funny how that works. Another intriguing result: the GTX 260 Reloaded outruns the GTX 280 in the GPU cloth and particles benchmarks. This result suggests Nvidia may be using only one or some subset of the GT200's thread processing clusters for certain types of work, such as vertex processing. In that case, the GTX 260 Reloaded's higher shader clocks would matter more than the GTX 280's additional TPC.