OP doesn't say how he's doing the comparison . . . to see multi-core performance you need to be rendering fast action (maybe Game or Video-footage), try rendering a 10-min video - that will show off the better performer.
FWIW my 2-core takes 5x (ie 50 min), but I do get a nice cuppa tea whilst it's doing it. However, there is a difference between Programs, so you'd have to be running the same software, and the same video-footage to do a straight comparison.
Be happy it's working OK.
(- and plan for when it ain't. )