I'm thinking with #2, it's the recirc valve. I get that a bit with the Corsa. Not that I think it's too much to worry about, but the Turbosmart recirc valve is designed as a general fit for the Borg Warner K0x and EFR series turbos, which are on a lot of cars like Corsa OPC/VXRs, just about all turbo Astras as well as the newer Ford Ecoboost engines in the Fiesta and Focus.
Thing is, the Turbosmart recirc valve has one single spring to suit all applications up to 30 psi, after which you can get another spring for the most insane applications. The Forge recirc valve, that has been the most common valve for the K0x turbo for many years, uses springs that are more precise in their operating range. It usually comes with one spring that works on a standard Astra engine (9-10 psi) and another for upwards of 20 psi for tuned engines. They have another two springs available for higher boost applications.
I think the Turbosmart recirc valve is more aimed at the Fiesta and Focus crowd (which run upwards of 18-21 psi stock, I believe), but that's not saying that it doesn't do a good job on a lower boost application like the Astra, which it does quite well.
Problem with running a BOV, is that most forget you need to remove and block off the recirc valve. You also end up usually bypassing the rear boost control solenoid, located under the intake manifold and in most cases, and there's mixed feelings in regards to the effect of the RBCS bypass, some are good, some aren't.
Honestly, there's nothing wrong with the RBCS system and the recirc system as it is now, you shouldn't have to fit a BOV, unless it's in a strict race application or you just want to look like a knob.