Kev, there are a few points I can think of that may be relevant here. But everything I’m about to write is all about stuff I’ve read, not from experience, so take that for what it’s worth 😉
First, if there is a substantial weight advantage to a tapered 11/32 vs a 5/16 hardwood of the same spine, that would be worth chasing. I don’t know if there is, my experience with wood is so limited.
Second, in the FOC seminar I’ve seen on youtube, Doc Ashby reckons all else being equal, tapered shafts get 8% better penetration than parallel. What penetration difference is there in 11/32 vs 5/16? I don’t know, but if it is less than or equal to 8%, 11/32 tapered is better, or at least on par.
Third, supporting your suggestion to use hard wood, is Doc Ashby’s 1st and most important point in that same seminar (and I’ve seen him say it here as well) is that “Structural Integrity of the entire arrow system is THE most important factor in terminal arrow performance. When structural integrity fails nothing else about your arrow’s design matters.” In the seminar he went on to say that the easy stand out for this is the hardwood shaft. I don’t remember the exact numbers, but it was something like 1 in 3 Al and C arrows mechanically failed on heavy bone strike, where something like 1 in 30 hardwood shafts failed.
The good Doc et al more or less gave us the specs for the best broadhead design, which Joe went and built, so an interesting follow up study would be to do some similar testing with the Tuffhead as the constant of the experiment and make everything else the variable. We know what the best head is, is there a best shaft to go behind it? If there is, what is it?