Yosemite on the MacbookPro mid-2009, slowest CPU is surprisingly spry on a SSD (Samsung EVO). The only two things I really miss are AESNI speed FileVault and updated SSH.
It's not going to set any records but totally usable for more normal tasks. What I really want is an up to date SSH without having to do ports/homebrew etc. so that I don't have to have exceptions for my setup.
Also, I'm really hoping Apple supports ed25519 in ssh in 10.11... No reason why this is not available at this point.