Dave, are you build a TRI-Y set up? If so, not to say that this is the case 100%, but you might be better off with a 1.75" secondary. We built a destroked 283cid to 252cid chevy V8 and engine dyno'd it with different headers along with other items, but as for the header aspect, the 1.75 sec. yealded a brouder more usuable torque curve. Also on that note in talking resently to Burns stainless in researching the header design for my 1uz swap in my supra in the event of not going twin turbo, that is also the sizes that they suggested for a TRI-Y setup. To me, it makes sence to go in even step up increments like what you proposed, but I guess that is not the case. Either way, if you have heard otherwise, I'd like to hear about it.
Chris