BOV can hold up to 24PSI (I have seen) it had the "crush mod" done to it tho, A quick google search will get you a "how to" for it. But I would stick with someone like Cobb, GFB (Go Fast Bits) or Turbo Smart for a quality BPV. Be sure that you get a By Pass Valve (like the stock one) that recirculates your air back into the intake, and not one that completely vents your air right to the atmosphere, its noisy and you could run into performance issue with it.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX