i'm not sure to be honest, otherwise we'd all be running bigger turbo's.
i think the problem is not so much the size of turbo but how it all flows.
1.6Bar of air from what ever source would be the same, to get to 1.6Bar of pressure requires the same flow through the inlet.
i think the inlet temps have more of an effect, a faster spinning turbo with smaller compressor will generate more heat and thusly higher act's and less power.
also the exhaust housing will restrict gas flow out of the cylinders and thusly use more power from the engine making it less efficient.
so as for power, you want a big compressor wheel and housing, along with a big exhaust wheel and housing, but you'll possibly never reach boost in this case, so a compromise has to be made.

i welcome any thought/evidence that contradicts this, so i can plan my next upgrades wisely.