The biggest improvement in gamespeed and fps should be in the "Hardware Class" line. setting it as a lower number _should_ improve performance.
3: Once game is loaded exit and QUIT the Battle.net launcher as well - it can be a memory hog and use some some hard drive cycles. Closing it makes your harddrive only use its speeds for Diablo
4: make sure you have any anti virus / malware scanners "scans" disabled while you are playing the game - again this will use the hard drive making your HD work harder - disabling them while playing should improve performance.
Hopefully 1 of these fixes work right for yourself.
P.S. Doing all these steps i went from 2-3fps in a game to no stuttering at all on my laptop - and the GFX card i am using is very very low-spec and slow.