For doing 300+ fsb, a good 2.40C makes up for a lot - no ****. A lot of it is the CPU.
Last and only time I had my AI7 up I did 300 fsb stable in all CPU and 3D benchmarks. However compared to the IS7 and IC7, it seemed a bit squirrely. I found it is more picky with ram too. ADATA PC450 that runs fine at 1:1 and 5:4 on the other boards did not top out as high. Now this was 4 months ago. Next time I get the board up I have water now, and I will update the BIOS.
As far as 5:4, depends on CAS timings. As we all know now, harder to do this with BH-5/6. As I have 300+ fsb CPUs now, I've been able to test 5:4 ability of various boards. On the AI7 I topped out at 290, 5:4, 2-2-2-5 with twin 512 MB XMS3500. I was using 3.1 VDIMM so that was not a factor. The board had hot restart problems above that so it's the Intel chipset limitation. I think one other guy also topped out the same. Now this is a 3D stable max, which is all I deal with. Many boards will boot and and are 2D stable at 5:4, 295-300+ but they will not clear an entire loop of 3DMark2001.
BTW, at 290, 5:4, 2-2-2-5 with my XMS3500 set to SR-Enh-A-D-D I got a whopping 3600+ unbuffered!!!
On the Epox 4PDA2+ I topped out around 289, 5:4, 2-2-2-5, with up to 3.3 VDIMM on tap. This was a major disappointment.
I am testing a P4C800-D now, and with OC PC3700 Golds Rev. 1.0 I top out at 293, 5:4, 2-3-3-6. Frankly, I don't think I will get much higher with BH-5.
I have hit 304-305 absolutely-stable-in-everything-you-can throw-at-it with an IS7, IS7-E, IC7, and did 300 on the AI7. It's all in the CPU here - you gotta get a well-behaved one. 66/33 fix is OK up to and including 302 fsb, and you just need to bump it to 68/34 above that. The Asus board I have does maybe 304 but it's a bit more work. The Epox maxed at 301.
I still need to test a P4C800-E and P4P800, but at this point the Abit boards are the most stable and well-behaved above 300 fsb. The AI7 not included, but I am wiser now and I think I will have an easier time at 300+ next time I get the board up.
I use a Tiger1 (7?) NB cooler with a bigger 40 mm fan hot glued to it. This thing is running 6800 rpm. I use either a Sparkle or Antec 400W power supply with pots bumped. When I was on air, I hotglued twin 50 mm fans to the shroud of my Alpha8942, blowing on the mosfets. I also have a 120 mm fan blowing on my ram.