Rig Suggestion.

guys i am planning to make a 4/2 gpu rig, basically a budget mining rig. So i did some digging and found out about Dell optiplex 390, Basically it can support upto 4 cards. One via pciex16 slot and 3 through pceix1 slots. I am going to replace its power supply with a corsair 1000 watts platinum one. The Dell optiplex 390 comes with 2nd gen i5 2400.. Will it be able to handle 4 cards easily? will it cause any problem to run 3x risers on this aged machine? Also i want your suggestions on whether i should get 2 RX 580s(8GB) or 4 970s, Basically it will cost me the same either way.

If i get 2 RX 580s then obviously i am going to dual mine eth and decred, but if the ethereum shifts to POS then i will be forced to switch to nicehash where obviously 4 970s will out perform the 2 580s. So is it worth taking the risk and going with 2 580s or should i go straight with 4 970s?