IMO the 2.23 is the most bang for the buck. Take the extra money you would have used on the 2.53 and buy an 80GB Intel X25-M SSD drive. The SSD will make any MB or MBP feel like a speed demon. 80GB may not seem like much, but take the drive that came with the MBP and out it into an external enclosure or spring for an OptiBay.