Pure speculation.. Says who? Turbosmart and people flogging their products?
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I've found no bov reduces lag between gear changes. Thats before and after. My assumption is that it must take longer to fill the IC and its piping than it does to bring the compressor back up to speed. Thats also assuming the pressure spike created due to no bov does reduce the compressors speed 'slightly'.
Its a falacy that the compressor stops/stalls or spins backwards.
Regarding drivability.. I've found no bov to cause the car to stall under some circumstances and pop/overfuel more when coming off the throttle. Apart from that the performance aspect its definitely worth while, I currently run WITH a bov because I don't like to blow flames at the cop car behind me nor do I like stalling.
Its possible a tune can prevent the pops and stalls, it was previously (Ceffy's, VLT's, XR6T (running high boost yes can their bovs) so I don't see any reason why it cant now.
Take it from a professional in the industry not the mega buck companies trying to flog off their product to you.
http://autospeed.drive.com.au/cms/A_1457/article.html
This has been covered to death and your answers have previously all been answered.