1) IN GENERAL OCing dualies does not work as well / as far as single boards. Its a chipset thing. MOST dual boards do not have vcore, ram voltage, cpu multi, and FSB multis as the single boards do. ALSO, even when you find a good dual board that OCs, it won't go as far as a single. For example, the MSIK7D (I have one) only goes to 150 FSB, so you won't get the memory bandwidth you'd get with say an abit kx7333 running at 210 FSB.
Of course, you in say the MSI you could up the multi, and so have a high multi with an FSB of 150, but this won't run as fast as a lower multi and higher FSB you could have on a single system.
BUT, IMHO, dual OCing to 150FSB is not too bad.
2) I do not know how big the SK7 is.
A) There are "holes" in the the MSIk7D for a HSF or waterblock
B) I have two thermaltech volcano 9's on my board, they LOOK big but I don't know how they compare to the SK7.
Generally, OC'ing duals is harder because of aforementioned lack of OC tweaks, not to mention that if you try to overclock two processors simultaneously, they'll only overclock as far as the speed of the chip that will OC the least. so if you have 2 XP1600's (seems to be a popular setup) and 1 overclocks to 2 GHz and the other to 1.8 GHz, 1.8 GHz will be all you'd ever be able to hope for out of those chips.
I've got two mildly overclocked Durons on my K7D Master - my brother has a 1.2 Duron of the exact same stepping that does 1450 in his setup (KR7A-133) but my Durons will only do 1320. I think my issue is a lack of RAM voltage tweaks. It doesn't like AGP 4x at this bus speed (110 FSB) but AGP 4x with 105 FSB is slower. I'm pretty sure it's just the RAM because core voltage is only at 1.8 and boosting the vcore won't get my CPU's any higher.
My system that is also based on K7D will work at any fsb setting except 150M mhz, but I cannot get it to run stable at any setting other than default.
I am using cpus with different stepping, Im not so sure if thats a good idea.
My experience with the MSI K7D Master has been phenominal! I love the way it overclocks and has been my favorite motherboard of all time since I got my first one and overclocked dual XP1600's to 1800 MHz! It's been running rock-solid ever since and is the fastest rig I have ever had. It blew away my single P4 @ 2.4 rig w/ RDRAM, so I traded that sucker for another K7D!
Duals aren't hard to overclock.They just don't OC very much yet.
They faster XPs and MPs have limitedOC anyway. Hopefully the 2400s up will help that.
With 2 procs I don't feel the need to OC much. The power is already there. But it is still fun.
As most have said, overclocking on a dual is easy. It all depends on the chip(s) and/or memory.
I currently have my system at 150FSB w/no problems and it is COMPLETELY STABLE (watercooling does help ).
My dual system is actually more stable overclocked than my tbird system. My t-bird system crashes in Prime95 after about 2 seconds if I even attempt to overclock it, while my dually runs completely stable for hours on end in Prime95.