Would my CPU bottleneck with one/both of these cards?
It should be good enough for a single graphics card. I don't know for sure yet, but I would assume the gtx 760 is going to give you the best performance.
As far as I know, the HD7870xt has about the same performance as a GTX 660. The 760 is pretty much an upgraded 660 (although I heard it's not that big of an improvement).
However, I strongly recommend getting a 7950, it's got better performance than both cards and it's 'only' 10-20 bucks more if you find the right one.
7950: http://www.newegg.com/Product/Product.aspx?Item=N82E16814202026
760: http://www.newegg.com/Product/Product.aspx?Item=N82E16814130933
7870xt: http://www.newegg.com/Product/Product.aspx?Item=N82E16814202024&Tpk=7870xt&IsVirtualParent=1 (this is the only 7870xt available from that site)
If you don't want the 7950, I'd go with the 7870xt.
Actualy, the regular 7870 compares to the 660ti, the XT falls slightly below the 7950 and 670, that's the same range the 760 is in. I haven't seen any direct comparisons between the XT and the 760, so I can't say for sure what's better. Although, there are some really nice coolers on the 760's, like EVGA's, Asus's, and MSI's, while sapphire's cooler isnt the best.
Im gonna wait until some reviews start rollin' in. I have a GTX 650 Ti right now, in most games not really amazed by the fps. So I was looking for an upgrade, and if these 2 cards aren't a bottleneck to my cpu then I think i'd go for the 760, just because. 7950 is out of my pricerange.