Check for obvious signs of abuse ... bent pins, brown 'scorch' marks on pads or pins, messy old paste, etc. Ask if the chip was over-clocked and what the volts/settings were. A Yorkfield C2Q would be a good bit more efficient and a tad-bit faster.
Check behavior coming out of sleep/hibernation. Monitor C&Q/Speedstep performance. I even check the maximum under-volt at idle and load.
I run an hour of OCCT at stock volts/temps. I use a build-specific triple-torture load test. Make up your own: Record an HDTV stream while running CineBench15 with 6 browser tabs open.
Putting it in a decent mobo with good RAMs will help, too.