If you are building a new system ALWAYS use the "C" models (266 MHz FSB). Technically the 200 Mhz models are a little easier to overclock, but the performance of the 266 Mhz fsb models are MUCH BETTER.
A 1400 (200 Mhz FSB) approx= 1200 Mhz (266 Mhz FSB) for most games. Office Apps don't show much difference.
Honestly though a 1400 Mhz Athlon will only get to about 1533 Mhz or so without some really extreme cooling. If you want to do better, get ahold of the brand new 1400 Mhz Athlon MP models.
(They will be renamed Athlon XP soon, and available at 1533 Mhz sometime in early October.)