By my crude calculations the TRUE Spirit 140 Power with 8mm pipes has about 30% more pipe to fin contact area than TRUE Spirit 140. That is assuming both measure 107.5mm from bottom of fins to top of press fit flange on top of top fin... Which is the length of fin metal in contact with heatpipe.
Fin area is about 13% less for TRUE Spirit 140 Power is about 13% less than for TRUE Spirit 140; 45 fins on TS140P compared to 51 fins on TS140.
What is interesting is much better the cooling is.
Lenny over on Bit-Tech tested it on his i7 920 @ 4.2Ghz using TY-143 fans. His testing shows TRUE Spirit 140 Power 0.3c warmer with one fan at 1200rpm than NH-D14 was with 2 of the same fans at 1200rpm. Both running 2 fans at 1200rpm the TRUE Spirit 140 Power is 2c cooler, and 2 fnas at 2500rpm it's 3c better.. Remember this is NH-D14 with 2500rpm TY-143 fans, not it's stock 1200/1300rpm fans. Stock TRUE Spirit 140 Power uses a TY-147 fan. Same performance as TY-143 at same rpm.
On an i7 3690x @4.5Ghz TRUE Spirit 140 Power was 0.8c warmer than NH-D14 SE 2011 65/4c to 66.2c). Also 3c better than TRUE Spirit 140 with 6mm pipes.
And at same time was 2.5dBA quieter (42.4c to 39.9c)