Should've thought of this earlier. I can't possibly fit a WDN4800(WiFi card) inbetween the R9 290's. But, possible solution. I've read that it's possible to fit a x1/x4 slot in a x8 slot. Now, on the Sabertooth 990FX there are 6 slots. 1 and 4 being x16 and 6th one is visually a x16 slot, but it's a x8 slot.
So, if I place my R9 290's in 1 and 4, and the WDN4800 in the 6th slot, will the 1st and 4th slot remain in x16, or will the 4th one become a x8?
So, if I place my R9 290's in 1 and 4, and the WDN4800 in the 6th slot, will the 1st and 4th slot remain in x16, or will the 4th one become a x8?