970 is faster than 290 and is nearly equal to 290x. So even if u r gonna play on bigger resolutions like 1200p and 1440p, u'l b absolutely fine with that build.
But if u can invest jst a little higher then go with 290x. I wont tell u to go with 980, coz even if its a beast, its still costly.
But remember 970 requires way too less watts than 290x. So if u r gonna go with it, it'l require min. 850-950watts psu. Or u can go with amd r9 300 series gpu, which will launch shortly in may b a couple of months.
About ram, the newer and upcoming games will be very hungry games, so u might need more than 8gigs in future. U can always add more ram as u need in future. But this is not necessary, coz the games will depend always on the vram of gpu...