The OP is not asking what system to purchase, P67/2600k vs. X58/920. That answer would be obvious. The new tech rocks and provides way more bang for the buck. Although the P67 is not the high end chipset and is a bit more restrictive than the X58 in overall bandwidth, it offers enough gains to compensate. On on the CPU side it's a No Contest.

That said, if I were sitting on a nice 4Ghz+ I7 with X58 set up would I upgrade now? Nope. The gain is there, but not worth the outlay from a day-to-day seat of the pants meter on one hand, while the P67 isn't all that enticing for the hardcore benchers either...especially the triple and quad SLI guys.

I'm sure more benches will come out showing both systems up to speed. There is no doubt the awesome Turbo Boost on the 2600k makes it look pretty great against stock speed I7 parts. But get both parts up to speed, and the gap narrows.

If I were sitting on a P55 with modest I7 chip, I'd consider the upgrade.
If I'm on an X58 and a solid I7 clocking chip, I'd sit this round out and wait for the performance chipset due out later.