I've been for a ride with you in the streets of mudgee, you took blackbart and I for a spin. Ages ago
Back to the topic at hand - Tex and I were debating this last night. When you're talking about how much power an engine's making in terms of the turbo side of it you care about two main things - boost pressure and intake air temperature. Remember that boost pressure is measured at the manifold, after the throttle body. Same with intake temp. At that point, everything else is constant because the heads are the same as before, the cylinder filling will be the same. This means that for a given manifold pressure you will get a constant VOLUME of air going into the engine whether your turbo is big small or spraypainted bright purple. With a bigger turbo, the air isn't heated as much and therefore because it's denser, you get more MASS air flow into the engine - which at the end of the day should give you more power.
As for why two stock turbos running 1 bar gives more power than two bigger turbos running 1 bar I'm not sure. It must come down to tuning differences or - more likely - dyno differences. Remember that dynos aren't comparable a lot of the time - you only have to see Secoh's "dyno proven" 195rwkW VW Beetle to know that dynos can tell fibs. (although I think that power figure was wind assisted)