My current system is 23" monitor (gaming on 1080p), i7-2600(non-k) on a z77 asrock extreme 4 mobo, 8gb corsair ram, 750w psu and a singlte msi 7870 twin frozr III gpu. I love the card and i have it OC'd a fair bit (no voltage change). Initially I wanted to buy the msi 7870 hawk edition to run cross-fire but someone told me i could use other cards in the same AMD family. Would a 7950 or even a 7970(which is slightly out of my budget range atm) be a better choice so i could get 3gb of vram instead of 2? and would me temps/noise decrease since i won't need to OC my 7870 too much?
you can CF different card with amd card but it still have restriction. you can CF any card between 7900 series but it will not compatible with 7800 series. plus combining cards with 3GB and 2GB VRAM does not make total available RAM as 5GB nor the system will see the system has 3GB of ram. for example if you're combining 7870 with 2GB ram with another 7870 with 1GB ram (obviously 7870 with 1GB ram does not exist so i just make it up so i can make examples out of it) the system will sees both card having 1GB ram available to each of them making the another GB available on the 2GB model completely useless.
as for the cross-family issues you can CF 7970 and 7950 together because both were based on the same chip, Tahiti. 7800 are using Pit-Cairn chips so they are not compatible with 7900 series.