Two different engines optimized for different purposes but in general Unity will run much better on low-end hardware than Unreal. Unreal has a renderer that is (out of the box) definitely aimed at high-end hardware.
KSP's performance is probably bound by a physics system that is abnormally complex for games. Unity's version of PhysX is based on an older, slower version. Unity 5 brings that up to date so if Squad decide to continue development on 5 there should be some improvements straight away. Unreal uses the same physics middleware out of the box.
KSP's performance is probably bound by a physics system that is abnormally complex for games. Unity's version of PhysX is based on an older, slower version. Unity 5 brings that up to date so if Squad decide to continue development on 5 there should be some improvements straight away. Unreal uses the same physics middleware out of the box.