AMD R7770 in Crossfire

In my new gaming PC I have 2 AMD R7770 GHz Eddition cards in crossfire. how much power should I expect out of them. My CPU is an AMD FX 8350 and my mobo is a Gigabyte 990fx UD7. I have 16GB of G Skill 1866MHz RAM. 128GB ADATA SX900 SSD. 850 watt Corsair PSU. 1TB Seagate HDD. and a NXZT Phantom full tower case. 

My question is why would you get 2 medium range cards and crossfire them to get 1.5 highend cards instead of just getting 1 high end card and going with that...

That can only really be determined with benchmarks. I would expect to see it getting somewhere around 80% of a 7870 GHz edition card. But remember man, it's almost ALWAYs better to get 1 more expensive card than 2 cheaper card. 7770 is a good card, got one for my boss, but I personally wouldn't recommend crossfiring them over getting 1 7870 for almost the same price.

yeah pretty much my point.

i needed more DVI ports so 2 7870 GPU was out of my budget.. i have 4 monitors. each has its own purpose. 

by the way i am a CompTIA A+ and Network+ tech. i mostly work on the network side. so i dont do personal builds often.