SSD, then RAM, then CPU is the way to go.  SSD will speed up PC the most, then you can decide if you still want more RAM, then I7 from there.  Hard to see much difference going from quad to quad core, but if you're a gamer or PC is under heavy load regularly, then you'll notice more difference with CPU upgrade. I didn't notice much difference going from dual to quad in previous PC.  But SSD and adding RAM made it fly. Make sure system is clean. May be you're just due for a software reload?  If you just bought the refurb, software should be fresh to begin with and system clean.
I have a refurb 7010 sff with core i5-3470. It is bios version A29 and system info in bios identifies proc correctly with core count of 4, but dang this thing is slow.When I go to multi core support in bios it list only two cores. My options are all, 1 or 2. Is this right, and 4 cores enabled correctly under 'all' selection ? Or should it show 4 cores in multi core support ?
Multi Core Support 7010 SFF