Quote:

build similiar room in each engine extract some unreal texture and use them in both engine and use same lights and unreals will look better




that is only for that in unreal the detail map is creata automatik for the editor.

therefore
build similiar room in each engine extract some unreal texture and use them
in both engine and use same lights and use the THE SAME DETAIL MAP and you observed less differences

can use 512x512 whit not problem