I finally found my little BBQ boar... it went down to my Ruger M77 MKII .358 Win carbine and a 200 grain RCL. Dropped straight down with zero flinching. I don't like the TSX for the .358 Win, standard cup and core bullets are right in it's wheelhouse... the TSX is better in the fast .35's. The 225 Partition is a good bullet if you are loading to MAX, but at moderate speeds, the 200 RCL, H-SP and Speer HC are just about perfect.
OP, I kind of like your .280 over the .300 WM, but of course both will work just fine.