Intel provides alot of support for various products and if yours has become dated, it maybe listed under some "legacy" support webpage. I have older stuff after googling the Intel being the primary source of hits I want and then go there. try that out as a means to get things done.
As for your questions, your mtrbd. has the latest bios updates support slower speeds, it should for higher speeds as well. The problem is, just how far that can go, but usually when a class of cpus are supported, they all are. Then the remaining limits are the FSB, etc.. Does the multiplier allow the speed you want to be obtainable, then the specs are the key, review them and match.
My current motherboard (Intel D975XBX2) no longer has active tech support on the Intel website. I checked the CPU compatibility chart and it listed the E6700 CPU at 2.66Ghz as compatible. I was shopping online and found several E6700's listed but at higher clock speeds. Will those still be compatible? I have flashed my MB with the latest Bios.