Is there any more way to squeeze out some performance out of my mid 2009 Macbook Pro 13"? I still like my mid 2009 13" Macbook Pro. It's solid and running quite well. However, since Yosemite things are getting really laggy and slow, so I guess that my hardware is getting a bit old. Although I swapped the old HDD to a 3rd party SSD and upgraded to 8 GB of RAM, I still see lots of lag and slowness especially when my 27" Cinema Display is hooked up via mini display port. Is there anything else I can do, in terms of hardware upgrade, to increase performance or is this just the end of the road for my baby?
I found out that there is no more way to upgrade in terms of hardware since the last option would be a new CPU which cannot be replaced in the Macbook. Overclocking the CPU is no option either for safety reasons.

However, upgrading Mac OS from Yosemite to El Capitan has greatly increased performance, so I guess I'm good for now.