I've upgraded 4GB 2007 iMac to Mavericks and it worked very well (for its age). Mavericks introduced RAM compression, so for RAM-constrained machines it may be

I've upgraded 4GB 2007 iMac to Mavericks and it worked very well (for its age). Mavericks introduced RAM compression, so for RAM-constrained machines it may be even better than the previous OS.