I wouldn't do that with am3+. I'd look to x99 for a rediculous setup like that. You would probably be better off with a pair of fury x's or a pair of 980tis that 3rd and forth gpu is not going to amount to much. Depending on resolution you will probably run out of vram before you even touch the surplus core power. You will need a beastly and high quality psu.
My friend just built a x99 (5820k) with 980ti SLi and it rocks @ 4k res.
If you need maximum RAM then 2 titan x's (although it is def not worth it imo)