For general "well performance", the speed of the Harddrive is most important. It would be the best, if you build in a SSD. Otherwise you have to take a look on the speed of the hdd. 7.200 R/min are much faster then only 5.400. But also louder an emit more heat.
If you don't want to render or do other really CPU-intensive jobs, you wont need an i7.
For games (not high end gaming), office and Internet an i5 is absolutly enough.
Better use the £90 for invenst in a fast SSD.