There's a lot to consider re Vista -> 8
Have you seen Windows 8 running? Don't upgrade until you have because it has some very big differences in the user interface. If you don't like the new "look and feel" as many experienced users don't (me included), there're some nice 3rd party programs to make it look and feel more like Vista and Windows 7. One is Start8, which is $5, another is Classic Start which is free. They both give you back the Start button and the things you're used to seeing there.
You will likely see a moderate speed increase with Windows 8 but understand the games have been removed FWIW. The only bug I've run into with Windows 8 is that the two desktop PCs I've tested it on don't wake up from sleep mode, so I just turned sleep mode off. There's probably a patch or BIOS flash for this but finding updates for my Biostar motherboards isn't easy.