heres your proof.....
Now, I'll admit with identical clock speeds, you will see a slight increase in performance with the larger cache. But I would still go for the chip that will give me the highest clock speed.
Even the recent E6400 steppings still OC well, I had to RMA a E6400 30B that was in my folding rig and got a 49F as a replacement. It tops out around 3.7ghz, but runs 3.2ghz @ 1.36vcore 29C idle, 41C load with a Zalman 7000CU in my HTPC with 0 air flow.