I don't notice a difference at all...
Iv a hybrid in my i5, and an HDD in my i7 (checks... yes) Steam is parked on a regular HDD on the i7....
Honestly, I notice almost No difference in performance at all.
The only time I do is when Windows is accessing the Swapdisk... the i5 takes a lot longer because the Swapdisk is on an HDD, and the i7 has a 32Gig (disposable/cheap) SSD with the Swapdisk parked on it. Difference in PC?... Very little... I only see a performance change in my Largest parks and even then only when I'm accessing the Scenery or Building menus.