Hi, for what you are doing, stay with the i5, put the money towards SSD storage, do not purchase a fusion drive, The new fusion drives prevent you from
allocating where your working from, we had both machines and we returned the i5 and purchased another i7 with a full SSD. The big problem with a fusion
drive is that when you have more than 128Gb of data on the drive you will end up using the HHD and as soon as you become accustomed to the performance of an SSD (Read Speed 685MBs) you will be very irritated with the speed of the HHD (Read Speed 115MBs).
The other problem is that the FUSION drive is not great at placing your data on the right drive so even with only 50GB on your drive you will still be using
some of the HHD, even something as simple as the start up, is slower with a Fusion Drive, (11 seconds slower than a full SSD Drive).
As to the performance of the i7 compared to the i5, it is very impressive, even with something as simple as rendering a 200mb photo in photoshop the i7
completes the task in 27.9 seconds and the i5 takes 46.6 seconds, (39.9% slower), Hyperthreading wow. Depending on how many cores are active the i7
is between 6 and 2 percent faster than the NEW MacPro 4 core.
Also, Mavericks is super memory hungry, if you are ever on your Mac for 6 hours or more get at a minimum of 16GB of ram, do not buy it from APPLE
purchase it from crucial (2 x 8GB = 16GB) and sell the (2 x 4GB = 8GB) that come with the iMac.
Have fun.