Wreckleford
I have fitted a SPEC-R dump valve to my EVO-6. For normal driving in town there is no real benefit, apart from the noise, which is not only is noticed by pedestrians, but also by Mr. Plod !!
There is also a drawback that if want to cruise on the motorway (contant feathering of the throttle) you may get an anoying constat chirp if you hover at the revs that the turbo start to cut in/out (approx 2700-2800 RPM on my car)
If you are interested in track days then I would say that the replacemnt is a MUST. With the amouunt of power that the evo has I defy anyone to 'notice' an addition 2 or 3 bhp. What you will notice is that the 'pick up' is much smoother when acelerating through the gears, and overall this will give you a faster lap.
Reagrds
Markja