It's not your BPV. The stock BPV is good well beyond the capabilities of the stock turbo, and is even fine for like a VF52 or BNR 16g. Your hiccup is probably from the tune itself, as it's pretty common (search for things related to hesitation). You'll find a lot of info on it.
The 50/50 will really not do anything good for you, as the car runs a nice full recirc setup.