You can't upgrade to a 7200rpm hard drive in the Early 2011 13" MacBook Pro. It is not supported. Period.
I tried unsuccesfully to upgrade the hard drive in my Early 2011 13" MacBook Pro to a 750GB 7200RPM hard drive. After several attempts with different hard drives I realized that the kernel panic that showed up was due to the lack of compatibility with the drives to the MacBook Pro. I had a Mid 2009 13" MacBook Pro that I did not have any issues with whatsoever. I sold that MacBook Pro and was able to upgrade to the brand new base model without any out of pocket cost. Upon purchase of the new 13" MBP I maxed out the RAM to the full 8GB. After 2 months of freezing, lockups, spinning rainbow wheels and having to force shutdown I tried one last ditch effort to see if a faster drive would help. After speaking with the Apple telephone reps and the Apple Store Genius Bar we discovered that Apple doesn't even offer the option of a 7200RPM drive on their website - a fact that I found quite disturbing. The concensus is that it is a power management issue that causes the incompatibility and the reason the drives are not offered on the 13" models. The problems I had were the end of the line for me. I just switched out that train wreck for the Early 2011 15" MacBook Pro base model. I got home and immediately installed the 750 GB 7200RPM Western Digital Scorpio Black hard drive and it was recognized within seconds. I'm back in business with gleeful abandon.
MacBook Pro, Mac OS X (10.6.7), Early 2011 13" MacBook Pro