That article is about how the GeForce is better for gaming than the Radeon, not the CPU.
A 200Mhz difference on the same class of CPU is a miniscule amount.
To be honest, you wouldn't notice much difference in gaming if you had a 2.16Ghz Core 2 coupled with the Geforce, let alone the 2.8 vs the 3.06. The GPU will run out of steam before the CPU.
You will be literally throwing money down the drain if you get the 3.06 and Geforce instead of the 2.8 and the Geforce.