400 strap is the easiest and needs the least amount of vMch and you can set a lower pl level than the 333 strap
the 333 strap is easy to but like i said if the you take a hit in the pl setting.
266 strap at higher fsb speeds you'll need more vMch. so say you run 450fsb and use the 333 strap
and need only 1.24vMch then you run 450fsb and use the 266strap it might require 1.30vMch