Here's my 2 cents.
My rig is a K-Mag 55#@28, and I draw 28.5 as close as I can measure. This is pretty close to what you are doing.
I had some arrows that were too stiff and already had the 125 grain broadheads, just like you.
I am shooting 2016's now, with the 100grn brass inserts, but I trimmed the full length shafts to 30 inches after bareshafting with the 100grn inserts just pushed in for test shots; they fit really tight. In fact I had to buff some of them a little with some 1500 grit to get them to slip into the shaft. After I cut to length I glued them in.
I too tried the variable weight points with the standard inserts, and found the heavier points to work better, and this is what led me to the 100grn inserts. I have not had any problems with that being too stiff, but as I said, mine are a little longer shafts anyway.
The brass inserts are maybe 1/2 inch longer into the shaft than the standard ones, I guess this is part of what others are talking about as far as internal stiffness, in addition to the weight being behind the tip instead of part of it. But the weight is still pretty far forward.
I also have 125g screw in snuffers and they seem to fly to the same point as the 125 field points when screwed into the 100grn inserts. (and mine are one piece, they don't come apart in any way)When I try the heavier test points now, I don't get any better flight, and definitely see the drop from the high end ones, the 175 and 200 grains. So I think I solved my problem with the inserts.
With the shorter shafts you have, you may well need to go for some more weight farther out to the tip, I guess. However, since you have this relationship with 3 Rivers, (who here doesn't?)if you wanted to try the inserts, you could get a dozen of them for $14 and try changing them out on a couple of arrows. I think I would put in a field point and heat that to let the heat soak in from the center, and try to pull it and the insert out with pliers. Who cares if I ruin the temper in a cheap field point? Then clean it up and put the brass insert in and see what happens.
If it works, it is cheaper than new broadheads, and if it isn't well you lost another $14, don't tell your wife about that either
.