I only have (6) data points:
Bell and Carlson round block Aluminum on Remington or Savage round bottom receivers shoot poorly for me in 7mmSTW and 280AI.
Drop in Whidden V blocks worked poorly for me in 300WM and 280AI
I built a homemade flat bottom Aluminum block for a 6.5-06 Mauser, and it shoots better than me.
I built a homemade drop in 20 degree V block for a 250 Sav on Sav action, it shoots better than me.