I'm a long time pc user looking to buy an iMac. I plan on going with a 27" 5k retina refurb. I think a 2 tb fusion sounds like a good option to go with along with 8gb memory to start. What I'm stuck on is wether or not to go with i5 or i7 processor and graphics card. I plan on using it for productivity and running windows in parallels. So any suggestions would be greatly appreciated!