I was looking at the 2600K+Asus P8P67 Pro deal and the offer is quite temping.
Here is a comparison i've gathered from a few indepth reviews. I've had my heart set on the Asus P8P67 Deluxe but the difference are:-
Asus P8P67 Deluxe vs Pro
Power design: 16+2 vs 12+2
Gig lan: x2 (Intel 82579 + Realtek 8111E) vs x1 (Intel 82579)
USB 3.0: front panel vs bracket
RAM
*: up to 2400MHz (latest BIOS)
*NOTE: 2000MHz RAM according to the manual runs at 1866MHz, nearest speed, due to the CPU somehow.
Also for the Deluxe: the Deluxe increased power design allows for better stability for overclocking, slightly lower memory latency and higher memory bandwidth (+5%), additional heatsink, better onboard audio, 2 more USB 2.0 ports, error diagnostic LED display, clear CMOS button, and reset and power on/off buttons for testing out the case.
I noted that on benchmarks with the 2500k
here, the Pro won as much as its lost vs the Deluxe. Where the Deluxe won, it was marginal in some cases.