If 100W over the required wattage enough or does overclocking require more of a larger PSU.
for your build which has a R9 290 get at least a 650 watts psu.
BUT.. the one you have on your part's list is a tier 3 (not a very good option and not ideal for overclocking), get the GS from EVGA which is a better tier 2 unit
or the EVGA G2 750 which is tier 1 (the best)
Thanks mate this has really helped me out! The list of recommended PSU's for graphics cards is very useful so now I will definitely be getting a 650W PSU.
would a seasonic 620w be enough for a evga 980 high overclock and a i5 4690k 4.2-.3?