This is such a difficult decision haha!
If you don't mind me asking why are you debating the fusion?
I don't know how much it would really do for me in the end. It sounds like a cool concept, but I'm not sure if it's worth the benefit for me personally. I get what it does basically, and see areas where I can profit from the drive, but when I was testing a previous generation low-end 27" iMac, I had no speed complaints really.
I think I will end up getting a Fusion Drive, just not 100% sure yet ; )
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I would get the i7 for longevity if nothing else. It won't make a huge difference, but it will make some difference, which will become more and more noticable as time goes on. I opted for the 2.33GHz iMac back 2006 over the 2.16GHz and it has given it more life in 2012. That's how it works! I would get a Fusion Drive and i7 with 2GB GPU if I were you. In prior generations, the i7 had hyperthreading and the i5 did not (8 threads vs 4 threads) which can make a huge difference for certain applications, including Creative Suite apps. I'm not sure if the current new gen i5's have hyper threading but if not then that's a major reason to put down the extra $200 for the i7.
It's still the same, only the i7 has HT, but from what I found during my brief search, you really need to have the specific programs and applications to make use of that.
I can only speak for myself, but the i7 seems to be an upgrade I would never need and I don't think I will use the computer for any major tasks in 6 years.