Jim,
I was pondering the same thing when I was setting up my416T and when the Lee dies arrived they included some load data, only XMR and Accurate powder listed.
Accurate 2230 with Speer 350grbullet, 68gr listed max.@ 2372fps.
I loaded 67gr and was getting 3" groups at 200yds so I took it hunting.
Sorry I didn't chrono my loads but that barrel is going back on for a more thorough workout here shortly.
Reloader 15 seems to be the most commonly mentioned powder for the 416Taylor but I have none...
Shoot me a PM if more Accurate or XMX data will help.
Link here for more info!