Do you really need to make huge projects like kite demo? Also if you touch any big objects (ie change it in any way), unreal editor marks it as dynamic until you rebuild lights. Then it will cast dynamic lights, that alone can drop framerate by 60-90% down.
I suggest you stop opening those show off projects from unreal, focus more on small templates and learning examples. Meanwhile get some more cash for upgrades, and wait few months before you upgrade, summer is coming you may drop whole unreal thing in few weeks. Also new, cheaper, faster, more powerful AMD graphics cards are around corner, even if you are not amd fan, those cards mean that nvidia will be forced to lower prices. You mag get soon something as fast as GTX980tI now for half of its current price.
So keep learning unreal, wait for new hardware out there.