Personally, I would treat such numbers as being useful only in relative terms. They help to describe the magnitude of tonal shift (among other things) between various cables. So, his 2% might be your 5% in absolute terms, however you'll both probably agree that the A/B difference between the "2%" cable and the "20%" cable is sufficiently large in a highly resolving system. I'd personally put the D5 much closer to the 20% than the 2% in relative terms after my brief listen to both, FWIW. That being said, I've never heard the cable that Dave describes as having "20% warmth".
One thing with the D5 is the character of the warmth is different vs copper so it's hard to compare... I would say the overall warmth is similar vs my copper cables but resolution/clarity is much better.