I was recently asking myself the same question. I ultimately stuck with the i5. I am a college programmer on a budget and didn't see the $300 upgrade as worth it. I think it's really going to depend on what you are doing. If you plan on working with CPU intensive programs, then it is probably going to be a good investment. But if you're just wanting to upgrade because it's a higher number, I would wait it off.
One other thing I would consider is, how long you are planning on keeping this notebook before you upgrade. If you are going to keep it for a few years and you have the money available, go for it for the sake of future proofing.