well, stock 660 (non-ti) will not boost that much and even if you go for it you wont notice the difference.
I'd say go for the cpu first (thinking you play mostly WoW)
But if you want an upgrade for the gpu also, go for at least 660ti or 7870xt. that will make you see the actual difference... no need to spend money for reference gtx660 chipset.
3570k is a very good cpu but you need to change your motherboard too, which will cost more cash.
go for amd cpu and save some money to get a amd hd7870xt gpu... (7870xt is a direct competent for gtx670, better than gtx660ti and costs a lot less)
(note1: also if you are not going to overclock no need to pick "k" versions of intel cpu's.)
(note2: 8350 and 8320 are typically the same cpu's with same features only difference is 8350 is clocked at higher frequency, if you want to save
cash you can 8320 and easily overclock it to 4.0GHz with Hyper212Evo air cooler for 20-30$ which will be better option imo)