Hello, I have a MBP 17" Mid 2010 model. 2.66 gHz i7, 8GB RAM. As I have been using rMBP 15" for the past three years, I feel this 17" computer too slow. Upgrading to EI Capitan does not help. I feel that it became even slower. It may be due to the hard drive. Is it worth to upgrade to SSD? Is the improvement in performance noticeable? About how many percentage of performance improvement will that be?