Just curious as I'm new to the Mac world...why wouldn't you upgrade to the latest OS? Is the machine older?
Late 2008 MBP, 2.4 gHz core 2 duo, upgraded to 8GB RAM and 512GB SDD, runs like a champ.
I'm usually ready to try the latest OS; I gave Yosemite a try, it slowed down the MBP (admittedly before I upgraded to SSD) so I went back to Mav.
Most of the really cool bells and whistles on Yosemite don't work on my machine because of its age, so I don't really miss anything.
Mav runs very smoothly, so I'm happy; might try Yosemite again after the 10.10.3 release. The lure of the new photos app may be too strong.....