If you like your rum and are comfortable with it take it by all means. There isn't a bear that walks that can't be killed cleanly with the 300 RUM and a premium 180-200gr bullet. I wouldn't think twice about taking the right shot with my 300 win mag with 180partitions or tsx. That being said though I did pass on a nice interior grizzly while carrying my 300 mag last year because I didn't like the hard quatering toward angle. I probably wouldn't have taken that shot even with my 375 H&H but the extra bullet wieght is reassuring.

What kind of hunt is it going to be, boat based or one where you will be doing a lot of hiking, it would depend on the situation which rifle I would take. A hiking hunt would be with the lighter more portable rifle, and boat based would be less critical of rifle weight.