Can a kind foci RS owner please help????

I am tempted to fit an atmospheric dump valve to my RS Foci - however got some questions......

Currently it has a re-circulating valve - does the dump valve effect the boost and turbo spin up time?? - the reason i ask is i was under the impression that the stored boost was reused and therefore effectively boost came on line quicker due to it being recirculated????

Secondly relating to the above - does this have an overall negative effect on the performance of the RS??

I'm in the middle of 'dressing up' the engine bay after having the car a year and am new to the forum so need some help!!!