[Moppie]

Another small point about the EVOs

The 7 and 8 use an anti lag system that recirculates boost inside the inlet and turbo houseing to keep the turbo spinning.
Fitting an after market wastegate/BOV can mess with this system, and actualy create lag.
(the US EVO uses mostly EVO 6 running gear, but may or may not use turbo and inlet designs from the EVO 7 and 8)

You only really need to ever replace one if as mentioned above the stock boost levels are to great, or the orginal one is to small and its putting back pressure on the turbo slowing it down off boost and creating lag as it has to spin back up again.
On any of the new Japanese turbos this is not a problem, and you should only mess with the wastegate/BOV is your doing something major to the rest of the intake/turbo/exhaust system.