I, too [would] use the 300gr XTP (Non-Mag) bullet if/when I use jacketed bullets at all. My experience shows that the non-mag bullet begins to loose integrity at velocities over 1500-fps, but does quite well at around 1300-fps. Not a problem since I dialed-down the power of my loading/shooting.
I "turned" to cast bullets a couple years ago and can't find a reason to go back to jacketed.
As far as performance, I've only "tested" any of my loads on deer. To date I still haven't found a deer that can stop a 300gr bullet of any configuration or at any speed and doubt if I will. Its been one shot/one kill all along so I guess they're getting 'er done.
I'm really too cheap to be willing to pay for XTP bullets so if I were to "go back" I'd look real hard at the Remington 300gr JHPs intended for the 45/70 ctg. I've sized them down to .454 and let 'er rip with very satisfying results but confess that I've not tried them at much more than 1500-fps.
Since I re-embraced the concept of good shot placement I've also re-discovered that when a bullet passes through the 10-ring, (heart/lung intersection) the caliber and power involved become moot.