Garand: Power Factor was one of my main considerations too, when determining which bullet/powder combinations would deliver best results for competitive loads. My "standard" 125 gr. bullet load comes in at exactly PF 100. With 105 gr. load at PF 84. So, no concerns, about meeting SASS Power Factor minimums. My little 105 grain "squirts" won't tip some heavy knockdown targets, either. Though very pleasant to shoot, otherwise. So it's nice to know the 125 grain bullet load can get the job done.
For those folks wondering how to calculate Power Factor for CAS competition, the formula is pretty simple: Weight of bullet in grains. Multiply by bullet velocity in feet-per-second. Divide this result by 1000.
edit: I ran into problems when running loads under PF 80, too. Across several bullet weights. Erratic ignition and accuracy....similar to what you observed.
Even with fast powders, like Titegroup. Trail Boss, Clays and other powders around that burn rate. As you likely already know, it's amazing what an extra couple of tenths of a grain of powder can do, to improve load performance.