All clock speed durons have the same cap of about 1000 mhz give or take for some exceptional chips, which is y i went with the 600, it's cheaper and got me to the desired speed. However, buying a 700 or faster is a good option because if you aren't able to o/c high or at all for some reason, at least you'd be at 100mhz faster than the cheaper 600... they also tend to run higher speeds at lower voltage.
The K7T Pro 2 is the one with the adaptec controller right? That's definitely a good pick, as well as the KT7 RAID or ASUS, wouldn't vary from those for features and performance purposes...
If you have the money, which isn't much these days with RAM, buy cas 2, yeilds 5-10% faster at the same FSB... also, if u buy 133 @ CAS 2 and FSB proves to be a useful way to squeeze some mhz's out of an o/c, u can pretty much be sure to get 143 cas 3, but with corsair i'd be disappointed if u didn't get 143 at cas 2...