Evidence has just come to light from aussie overclocker James who has managed to take his DFI LP DK P45-T2RS PLUS motherboard all the way up to a staggering 693MHz.
The validated CPU-Z screeny indicates an E8500 to be used for the task, with its multiplier set to x6 which stills brings it up past the magic 4GHz barrier to 4161MHz. Further complimenting his record FSB achievement is the trusty Crucial Ballistix memory ticking away on a 1:1 ratio.
It really is quite amazing to see just how high some of these P45 chipsets can go. You can view the validation page here.