First let me tell you I know what I am talking about.
I owned a 02 Stage 4.5 WRX. (403 awhp)
I owned a 04 WRX STi.
I now own a 05 WRX STi.
At the end of the 1/4, there is no way in hell a bone stock WRX will outrun a bone stock SRT-4. Assuming the drivers are both about the same skill level. The WRX will have the starting line advantage, but not as much as some may think. You just can't launch a WRX due to its glass tranny. Now the STi is a different story.
To solve your BOV question. It makes no improvement in power. If anything it can cause a lean condition between shifts if it is atmospheric, which is detrimental (however small the detriment may be).