Had a reply for mystic_1 almost done, and then...brown out.
The quick answer is that sizing and restriction in street terms are relative, but that's not my style so here goes.
My starting point was I wanted to use stacks, and this would also sidestep a major tuning issues with pods. Basing my stacks on the stock ones, means Honda has done 95% of my stack engineering for me. It was a given that re-jetting would be required, if for no other reason than the pipes I'm using.
I have my own ideas what this might be, and Terry will be letting us know what 'real world' testing reveals.
Restriction as you have pointed out can be good, but bad at WOT. This filter's available surface area is more than adequate for any 750+ at WOT. So the issue came down to the real world questions - how big a filter can I fit on the 550, and will that work on a 750? This is were current
racing filter theory comes in. In an ideal world you want the minimum interior filter height to be equal to the carb throat ID. This space allows (flow dynamics) for the centre of the air column to fill. Which is critical to promoting good fuel atomization, particularly at small throttle openings. In racing more is better, but this is for the street so space restrictions come into play. On a 550 the throat ID is 36mm, and 38mm on a 750. So that translates into a 45mm filter for the 550, and 50mm for the 750. I can get 45mm to fit the 550 (but very tight), 50mm doesn't because of the frame rail(s), and clutch cable. So question one is, on the street does that 5mm make a difference with the 750+. That's one of the questions Terry will answer. How? By using a spacer to 'lift' the filter's 'ceiling'. If there is a difference it will be at slow speed, and part throttle roll-on, because once on the mains only, different parameters come into play. This gets back to your comment about intake vaccum creating venturi velocity. The piston descending on the intake stroke, is you sucking on the straw.
The air sitting in the 'sized' filter is the so called 'still air'. So to get a crisp throttle, from my experience, with no slow speed flat spot coming off idle requires two things. That the initial air column filling the carb be smooth & solid, and the jetting matches the engine's mixture requirement. With a stock air box, and jetting (stock engine/pipes) those requirements are met. This the area that I'm concentrating on. The stacks remove one variable, initial smooth flow, which is were pods only fail miserably. The solid requirement is 'ceiling' height (see above
. Which brings us to the slow speed jetting needed with this filter to get a good idle, and off idle throttle response. I have my thoughts, Terry I'm sure will have his. From 1/4+ throttle on the question is only how big a main do you need to not be lean at WOT.