450- Sean used a 45/70 marlin with 400 TSX , good shot tough bull. At the extra velocity the #1 would drive the 400 it would work better.
To put the recoil and flip into a perspective I fired the 500 loads out of my mates #3 didnt shoot it twice. In fact never fired his #3 again. heres acouple of pics of Seans bull and projectile recovered both lobes of the lungs high and forward nearly missed the lungs.
Mick

Sean Chick 45/70 400 TSX

200 .35 barnes 200hornady 250hornady 400TSX/buff side view

End view .35's from boars