Both will work well. Season is closed most places, so I assume you mean next year or are hunting manged land. If so I would load the 25-06 with plain old Hornaday interlocks. The SST worked fine in the .280 but have more confidence in the standard version for more consistent performance.

The 25 seems to have more juice to it but the paper ballistics don't show much difference. Even so W Tx Mule deer are very solid animals going about 200 lbs. live weight, sometimes larger.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli