The BK, once the 5th injector had been 'neutered', is a nice controller, and was my preference for the 96 B4.
It does have limitations, but provides better driveability and fuel economy (post 5th injector defeat) than the GQ.
The cracking pressure difference (190 bar for the injectors intended for the BK, 220 bar for those intended for the GQ) is so small that the effective delay in the injection timing event will not be detectable. The fuel pressure ramp up is such that the time, (or fractions of a degree) difference between reaching 190 and reaching 220 is minuscule. Both of these are 300 bar full open bodies.
I had both BK and GQ, and freely mixed them in combination with 190 and 220 bar bodies (and with stock and Sprint 520 tips) without the idle symptoms described.