The processor
The larger L2 cache means that the transistor count in the Core 2 Duo MacBook Pro has been expanded from 151 million to 291 million. This allows for an increase in cache-to-processor data transfers, maximizing main memory-to-processor bandwidth and reducing latency.

Additionally, Merom sports a slightly deeper pipeline than Yonah (increased from 12 to 14 stages), which also helps to increase clock speeds. However, just like the Yonah-based MacBook Pros, the chips inside the new Merom models are soldered to the main logic board.

AppleInsider | A closer look at Apple's Core 2 Duo MacBook Pro