When editing video there are a couple basic things you should do to get the best performance out of your system.
1. All media should be stored on an external hard drive seperate from the drive your application is installed (i.e. your internal drive)
2. The drive you store your media on should run at 7200 RPM, should you chose a hard disk drive (not Fusion or Solid State)
Personally I would get the i7 with the fusion drive just because it would be a faster computer. But I also suggest purchasing an external hard drive to store your media on.
However, if you are on a budget, then go with the i5 and purchase an external drive that runs at 7200 RPM.