ok...
final result. using my boost controler set in "external wastegate"mode onto the stock bov's
it workes really well and holds boost very steadily. no spikes or anything
the turbo still makes the same noises so its not overspeeding.
but... i rekon i lost about 60kw posibly due to turbine back pressure.
so summing up. it works well but you loose power compared to using a wastegate style boost control.