To keep your over all PC cooler, yes it will help, if your 290 is a reference model it will help also, not knowing your old case and fan setup the difference could be from a few degrees 1-5C to 10-15C at best. You should probably setup a custom fan profile on the 290 using AB or Trixx as it would probably help most.

Mine only hits around 80 in an NZXT Phantom 820, with all the fans at their lowest speed (1x200mm top, 1x200mm front, 1x140mm rear, 1x200mm side), and my 290 on auto fan.