Mako,
I'm not talking ignition problems with hotter primers, just consistency. Actually, the reason I would like to load 44-40 with rifle primers is because of the greatly reduced sensitivity, not any performance advantage. In tube magazine rifles, rifle primers are a lot safer because they are so much less sensitive. A slightly high primer is less likely to go off in the magazine.
As far as consistency, the tests I've run have been with Spencer 56-56, 56-50, 50-70 Govt. and 45-80 Long Range Springfield. The Spencer rounds have about the same capacity as 44-40. When shooting black powder, a switch from regular LR primers to magnums almost always results in lower Std. Dev. in my limited experience. I haven't tested a 44-40 with large pistol and LP mag. The only one I own at the moment is a Whitney Kennedy, and it's a tack driver with pretty much whatever you put in it, so I haven't done a lot of load development on it, but I am very careful to check proper primer seating.
That's just my experience, for what it's worth.