All this sounds good, and different enough that we should make a seperate statblock. We can give them other minor alterations, too, like letting them overcome more hardness, give them DR and SR, that sort of thing.
Also, I think we miscalculated the skills for the regular spiders. As outsiders with an Int of 16, they should have 11 skills or more. I must've confused 'em with elementals at the time, as I said "5 at 13 ranks". So suggestions for the remaining 6 skills?
Ok, we have ranks in Hide, Move Silently, Listen, Spot, and Jump. Let's also give them Climb (just to make them very good), Balance, Tumble, Intimidate, and maybe Bluff or a Knowledge?