External Wastegates: Big or Small?

[sleepydsm]

I've got a 14b powered 1g AWD, all stock. I don't want to bother with boost creep, so I'm planning on getting an external gate o2 housing when I get my 3" turbo-back, and ditching the internal wastegate. I was going to go with a 38mm Tial, with a 1 BAR spring. But somone I know says I should go bigger. Isn't there such a thing as too big of a wastegate, espcially on such a puny turbo? The car will normally be at 15psi-ish on pump gas, and whatever on race gas.

-KEVIN