If it's just the highback that's the issue it's fine for Bear. Will you be hard charging Mammoth at mach speeds? Who knows but I see people with noodles riding in bounds. You'll be fine. If you are that worried, for just a little more you can get some K2 Formulas which will hold up better all-mountain.
Just got back from Summit yesterday and bombed the mountain on a 145 shank. Yeah it's crazy looking down and not seeing much board but there are short steep sections then a lot of mellow sections and the steeps aren't that steep.
What board is this going on?