Yeh I was going with 3x to start with but thought it would be better (not to mention cheaper) to go with 2x 290 for now and see how it goes, the cost of upgrading the PSU to a 1200w and a 3rd card increased the build cost quite a bit so decided 2x 290's would be enough for what I'm trying to achieve for now and if it works out ok I can reassess if I want to invest more.

Will I be ok to run 2x 290 on that mobo without risers to start? Been a long time since I built any PC's so don't want to burn anything out.