Stoney the N has a longer wing then the D models. Roll rate should be better in the shorter winged models. The M model had shorter wings then the N.
Excerpt from Widewing's website:
"The XP-47N took to the air for the first time on July 22, 1944. Test comparisons were made with a P-47D-30-RE throughout the early portion of the evaluation period. Much to everyone’s surprise, the XP-47N, with its greater wingspan and higher weight actually proved to have better roll performance than the D model. At 250 mph TAS, the N attained a maximum roll rate just over 100 degrees/second. The P-47D-30-RE could manage but 85 degrees/second at the same speed. At higher speeds, the N widened the gap further. In mock combat with a P-47D-25-RE, the new fighter proved to be notably superior in every category of performance. In short, the XP-47 waxed the venerable D model regardless of who was piloting the older fighter. The new wing was part of this newfound dogfighting ability, however, the more powerful C series engine played a role too. The additional horsepower allowed the N to retain its energy better than the older Thunderbolt. Perhaps the greatest performance increase was in maximum speed. Though not as fast as the stunning P-47M, the heavier N was fully 40 mph faster than the P-47D-25-RE and could generate speeds 30 mph greater than its principal rival, the Mustang. Scorching along at 467 mph @ 32,000 ft., the N could not be caught by any fighter in regular service with any air force on earth with the single exception of its M model sibling."
And yes, they did use 72" of MP during takeoff and climbout during combat missions. Try
http://www.inpayne.com/dad/ickyandme.html for a link to a story about a pilot taking off from Ie Shima's short runways loaded for a trip to Japan and back. Per the POH for the P-47N, the aircraft took off with enough water to run 72" of MP for 15 total minutes, even though it was limited to 5 minutes at a time. At lower MP, you could run water for longer than 15 minutes.
Last, my reference to rate of climb on WEP was not made with regard to climbing out after takeoff, it was made in the context of a combat situation where those 2800 HP give you a climbing advantage over the D models.