Well, I don't know about that second one, but the first one I may know. I've seen spread spectrum before but not for pci-e. Supposedly, spread spectrum is something that varies frequencies slightly during operation to eliminate interference from other signals going on in the system. It varies it in such a way that the signal can be "tracked" and distinguished from other nearby signals. On my board, the spread spectrum has to do with the chipset, I don't have pci-e on my board.
It's usually OK to turn it off. In fact, I overclock my rig, and it's actually recommended to turn it off in that case (for the chipset, don't know about pci-e). I guess when your overclocking, spread spectrum can hurt more than it helps. It's probably used to keep your vid card from receiving interference from the other nearby signals, probably wouldn't matter if you turned it off though. I noticed you already have it off, probably should leave it that way, if you turn it on, it could possibly hinder your vid performance? I would only turn it on if you have problems. Sorry can't help you with that other one though.