You should be okay with 4WD in October/November, cause major snowstorms don't generally pass through there until December or later. Generally, the "Chains required" advisory means "Chains or vehicles with 4WD"; "Chains Mandatory" will mean they actually want the chains on your tires (if that's in effect, you probably don't want to be driving anyway). CalTrans will keep the pass open as much as possible, but it will close if there is a heavy downpour--you may want to check conditions first if the weather seems iffy.
I was just through Donner Summit last weekend. Pavement around the actual summit is *really* bad--I think it might actually be original concrete from initial interstate construction. There is road reconstruction going on in a couple of areas to put in new concrete, including an area just east of Donner Summit and another area near the Nevada line; lanes are *very* narrow through the construction zones. I'm not sure when these projects are supposed to wrap up.
