Let's keep it simple: the Socket 1366 platform is obsolete. The turbo modes are very limiting and the three channel memory setup gives only a slight advantage. Of course, Socket 1366 CPUs don't come cheap either. The quite new i5 CPU is much easier to overclock and it's not that hard to achieve higher memory speeds.
Considering system cost, then the P55 platform is the clear winner. We have already proven that Hyperthreading/SMT is more or less a marketing gimmick. It works only with very few applications and in highly optimized applications such as x264 or games, it decreases performance. That's also the reason why we did not consider to use the i7-800 CPU series for this review.
Looking for the best performance money can buy, we recommend the i5-750 CPU. If you need SLI or Crossfire, shop for boards with an additional NF200 chip to get the most out of your two graphics cards, otherwise the P55 does just fine.