Interesting article @megan, I had no idea about the drag differential between a P-51 & and a Spitfire. Quite an eye opener! The cooler drag in particular is interesting, even with the 'meredith' radiators, the difference is that high?
In Paul Stoddart's article, he references use of the rear tanks making the Spitfire directionally unstable; didn't the P-51 also have this problem, and wasn't the guidance to always use the tanks in the order rear -> drop -> main? It wasn't isolated to these aircraft though, I remember reading about use of certain tanks in the Blackburn Firebrand being forbidden due to their propensity to 'spin in under power'