The wastegate is the best way and the most efficent way of regulating your boost pressure. A BOV, will just dump compressed air (it take HP to compress 30psi of air). The wastegate will allow (regulate) the hot gas to bypass the turbine and will not increase drive pressure (egt's). Wastegate work differently in twins as your sharing the hot gas (energy, or work) between two turbos and trying to keep your drive pressure as low as possible but still build boost efficently and as fast as possible. As far as I know, if everything is the same between a turbo thats wastegated and non wastegated turbo, the intial spool-up should be the same. Thats assuming that the wastegate is closed tightly. I've seen new turbo that the wastegate did not tightly close and leaked exhaust by the turbine. If your bored, one you should remove your turbo and see how the wastegate works. I thought that I had mine set at 22 psi, but it start-ed to move at 28psi. It took 40psi to fully open the wastegate. The new turbo opened at 22psi and fully opened at 28 psi. I learnt that you can't take something out of a box without a good look over.