Just an opinion that you must take with a grain of salt because I only have experience with an ST6. In other words, the following are my thoughts on the ST6.
I have had an ST6 for about three weeks now. I am using it with a 1.2 Gig Tualatin. It is running stable at at 1.5 Gig (125 MHz) FSB.
It is an excellent board for overclocking because of the flexibility it allows for setting up the CPU. The option for a 1/4 divider became especially important to me because my new Adaptec 2930 SCSI card seems to be intolerant of even slightly over rated PCI bus speeds.
I have a full compliment of expansion cards (modem/vodeo capture/NIC/SCSI/audio/video). With all other previous mobos it was always a nightmare to find the right combination of cards in the right PCI slots so they would all peacefully share the available IRQs. With the ST6 I simply plugged in the cards in the order I reached for them. I do not know if the credit goes to the ST6, Windows XP, coincidence, or a combination, but everything worked perfectly without the need to juggle cards in the PCI slots.
I did have to flash the bios on this brand new board before it would properly recognize a Tualatin CPU. It was shipped with an older bios that did not know about Tualatins.
Its quality of construction appears excellent. It has an integral RAID controller but I really do not know how frequently users will take advantage of this feature. I would expect to disable the integral sound controller and use an expansion card because the audio controller is also very intolerant of an even slightly overclocked PCI bus. At 112 MHz FSB (1/3 divider) seriously noticeable audio distortion was very apparent. At 120 MHz it simply crashes with a short glass breaking screech, then silence.
The board is somewhat wider (front to back of the case) than my previous P3V4X. In smaller cases this might make for a bit of overcrowding.
It also has numerous other nice features like a conveniently located USB header so you can take advantage of front of the case USB ports. It does not have fan control available. My Enermax power supply has a fan that can be cycled as needed by the mobo. The ST6 does not support this feature.
The distribution CD that comes with the board has something called Hardware Doctor that appears might be a very useful hardware monitoring software package. Unfortunately it is 100% incompatible with Windows XP (per Abit and my experience). No upgrade is avaiable.
I hope this provides you with some useful information.