Alright, you may already know this, but I just want to outline something first...
The bus speed on Pentium 4 motherboards is quad pumped, so if you have a Pentium 4(A) processor, which runs at a FSB speed of 100 MHz, then the motherboard's bus will be 400 MHz. The Pentium 4(B) chips run at a FSB speed of 133 MHz, so motherboards running these chips operate with a bus speed of 533 MHz. The new Pentium 4 processors that just came out operate at a FSB of 200 MHz, so the motherboards running these processors operate with a bus speed of 800 MHz.
Remember that these speeds are all at default, non-overclocked speeds. So lets say you have a Pentium 4 B chip, but you decide to overclock it. Since the only way to overclock Pentium 4s is to increase the FSB, you'd increase the FSB, up from 133 MHz to...let's say 150 MHz. Since the FSB is quad pumped on P4 motherboards, your motherboard be operating at a bus speed of 600 MHz (4 x 150 MHz). Now if you were really, really lucky and got your hands on an insanely amazing overclockable P4, and bumped the FSB up to 200 MHz, you'd be running at a bus speed of 800 MHz - just like the new Pentium 4 processors do.
With the Abit BH7, you have the option to run the FSB @ 200 MHz (thus an 800 MHz bus), and probably even higher - I don't know how high you can set it for sure. I have an Abit IT7 Max 2 Version 2, and with this board, you have the option to run the FSB anywheres from 100 MHz to 250 MHz (bus speeds from 400 MHz, all the way up to 1000 MHz). So yes the IT7 supports the 800 MHz bus.
However, if you read
this article, it says that the BH7 is compatable with the new 800 MHz Pentium 4 chips, but shows that all the other i845pe motherboards tested were not able to use the new Pentium 4 chips. They didn't try to run one of the new chips on an IT7 motherboard, but chances are that it is unable to use the new 800 MHz P4 chips.
The new motherboards that use the i875 chipset (Canterwood motherboards) are designed for use with the 800 Mhz P4 chips, as well as the 533 and 400 MHz chips (they're backward compatible with other Northwood chips). Also, the new 800 MHz Pentium 4 processors all have Hyperthreading technology, whereas the only other Pentium 4 chip that has Hyperthreading is the 3.06 GHz Pentium 4 B chip.
In terms of overclockability, the 400 and 533 MHz bus Pentium 4 chips have both been fairly good. That's really an overgeneralization because there are different makes (S Specs) and steppings (like B1 and C1 steppings - (the C1s are generally better overclockers)) of each processor, so it's really hard to tell, overall, which type of P4 overclocks better.
If you want to go with a chip that has HT technology, then you either have to get the 3.06 GHz P4 (@ 533 bus), or grab one of the new 800 MHz bus P4 chips, along with a new motherboard that will support the chip.
In terms of overclocking the new 800 P4s, it's still still too early to tell how well they will overclock, and it's hard to say when all of the bugs will be worked out of the Canterwood motherboards (you've got to see
this). So it's not advisable to purchase a Canterwood-based motherboard and an 800 MHz chip just yet, but at the same time, I would't recommend you buy a 400 or 533 P4 either, since they're becomming more and more outdated every day now (not really, but they're not the newest anymore). I'd say wait a while, if you can, for a Canterwood board to come out that gets good reviews, and then make your decision.
...whew... hope that helps.
