You'd be far better off matching them based on percent of original capacity and internal resistance. A 3200mAh cell worn to 2600mAh is in far worse shape than a 2800mAh cell worn to 2600mAh, though you'd probably also see a big difference in internal resistance between them. You might also consider checking IR at various states of charge, if you're being comprehensive.

... and at that point, short of massive automation in a fireproof area, you're almost certainly going to come out ahead buying new cells.