Well, I skipped the last page of posts, but I'll add my thoughts anyway
If there is a difference between a single-filtration straight print and a split-grade print that have been carefully contrast-matched, it could only be because the paper reacts slightly differently to being exposed to only the extreme ends of its sensitivity spectrum than being exposed to a continuous spectrum (however filtered and attenuated).
The way to test for this would be to make a print of your step wedge with, say, a #2 filter and then make a split-grade print using just the #00 and #5 filters that matched the
overall contrast range exactly. That means you'd really have to refine exposure times between the two filters and overall exposure time to get precisely the same density on the stripes of your step wedge at the very black and very white ends.
Once you've done that, you can compare relative densities of all the intermediate steps, plot curves, and see if they vary significantly, i.e., if there is a marked change in contrast-curve shape from one to the other in the intermediate range.
The concept of the test is simple, but the devil will be in the details matching up the densities of the extremities. It may take a while to get a split-grade print to match, i.e., render exactly the same densities on the high-density and low-density stripes just above Dmax and below Dmin. Once there, though, measuring reflection densities and plotting the curves should be routine.
My guess is that you'll find very little difference in curve shape between the two, but that's just my gut feeling.
Best,
Doremus