It's a shame that Barnes doesn't make the 250 grain bullet anymore. It hits like a Mack truck. I bought the last three boxes they had at the factory years ago and reload and replace the ones I use on game to keep my quiver full. My 350 Rem Mag pushes them at 2500 out of a 22" Bbl. Every grizz I've put my crosshairs on have dropped in their tracks thanks to that bullet. I'd look at hammer bullets for something similar as your whelen with the ability to load them long would easily push 250 grain bullets to 2550-2600fps and possibly more with the new powders available.
I like the Barnes 225gr TSX bullets out of the Whelen, they are deadly on black bear. They are doing 2700fps out of a 22 inch barrel. I believe that 35 Whelen ought to be enough for a grizzly, however if I were going on a planned hunt I would be using a 338WinMag or a .358 Norma mag for the hunt. I like the 35 caliber bullets for bear hunting, have had very good performance with them. I use the Barnes 200gr TTSX in the .358 Winchester, never had to track a bear, terminal tissue damage, always a through-and-through.