Will This Cut It?

I'm planning on getting an upgrade before the release of Battlefield 4 as I'd like to play it in all its glory in Ultra graphics. I was planning on getting two 7870's and running them in Crossfire (I know everyone says get one card but two performs better on Battlefield and it's basically all I play).

Do you think my CPU will be able to cope with that? I've heard the term "CPU Bottlenecking" and have a rough idea of what it is but don't really know much about it. I know that if I get it I'd have to overclock my CPU but do you think I'd have to do that for this build?... And if so then by how much?

I'm sitting here currently running with this setup. 

AMD FX6100 (3.3GHz)

Gigabyte GA-970A-DS3

Corsair CMX4GX3M1A1333C9 4GB (x2)

Asus HD 7770 2GB

Corsair CX750


Around the 4ghz mark should be attainable with the right cooling even on that board and would see an improvement compared to stock clocks. 2x7870's will be fine. BF should perform very nicely indeed.

Any recommendations cooling wise? I've never purchased liquid cooling before, think I'd need that or just a hella lot a fans?

Depends on what you can fit it your case, ideally if you have the room a corsair H100i is a good choice, below that the all-in-one cooler range inst really worth the prices that they go for. Im really liking the new noctua range though like http://www.techpowerup.com/reviews/Noctua/NH-U12S/ for the size they are incredible performers and really quiet.

If you head down the dual gpu path, yeah have as much airflow in your case as possible. Hitting that pocket of space between the cards is crucial. Heat pooling there is a real pain. I would balance though the airflow rate / noise. Even at lower speeds most fans will move a decent amount of air.