Bottom line...do what you're interested in. If you're interested in research, then work on a project for six weeks. If you don't like research and are just doing it as a CV filler, it's probably not worth it. Yes, PD's like to see that you've done some research, but unless you invent an L-spine implant or something it won't stand out. It's hard to complete a kick-ass standout research project and get it published in six weeks, and nobody cares at all unless the project is published.

If you're trying to decide how to best use this time to get into residency and that's the only issue, then do another rotation somewhere. That's where the money is. Even if you're in love with your home program, don't put all your eggs in one basket. The best way to ensure a spot somewhere is impress the hell out of people during a rotation with them. You'll have a huge advantage at any program if they know you and thought you've done a good job....as long as you don't knock up the Chairman's daughter or something.