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It's generally accepted that Yosemite is a bit of a pig, and that the new El Capitan version of OS X sorts a lots of things out. If you can wait until later this autumn, that version will be officially released and you should see things speed up. If you want a sneak peak and can deal with beta software, there is a public beta of El Capitan, which even in beta is being reported as better in many ways than Yosemite.
i have maxed ram and SSD already - when i upgraded to yosemite everything just s l o w e d d o w n loads, so I thought, you know what, lets just back everything up and start again.
tldr - i have a child and cannot afford a new mac.