I upgraded my late-2008 iMac with Mavericks to see if it performed better than Mountain Lion given that my machine's maxed out at 4GB of RAM and my experience thus far has been that overall, the system is more responsive, but there's a lot more latency in doing things like restoring backgrounded applications that haven't been quit, but are still running. It may be that my machine is too old, but Mavericks has just shifted the latency around in this case.