VR-Zone has done some investigations on the newer A3 stepping vs A2 stepping of the GeForce4 Ti4600 GPU.

Using the Dragothic high detail test which is one of the most demanding 3DMark2001SE tests, i repeated the test 5 times to check out the stability of the core with an overclocked core clock. GF4 Ti4600 A2 stepping was able to pass the test 5 times at 320Mhz core clock but fail all at 325Mhz and the A3 stepping was able to pass the test 5 times at 325Mhz but not 330Mhz core clock.

Read more