John
I could not source a decent controlled round action suitable for .416 Rigby within my budget back in '91, I was not enthused by the Remington or Ruger rifles on offer at the time. Uncle Nick ran an article about 1990 about the .416 Taylor with plenty of load data. I started with an unwanted Zastava .458 & re-barrelled.

You will love the .404, I would choose this chambering if it were today, the.404 can be loaded to much more power if you so desire!

I agree that anything over 2100fps with a 400gn projectile is plenty for buff & wild cattle. I have found the Woodleigh softs more reliable penetrators when impact velocity is 2100-2200fps just as they advise.