Montana already has 15 designated wilderness areas making up a total of more than 3.4 million acres. This figure doesn't even include the 1.4 million acre Glacier National Park which the majority of the park is treated as de-facto wilderness just the same as Yellowstone National Park is treated. Autos allowed on a few roads, and the park also contains a few commercially developed areas, but other than that GNP allows no motorized use.

The largest wilderness in Montana is the 1 million acre Bob Marshall Wilderness which is southeast of the proposed 171,000 acre Winton Wedeymer Wilderness. There is also the 73, 877 acre Mission Mountains Wilderness to the south and the 94, 272 acre Cabinet Mountains Wilderness to the west of this new proposal.

http://www.wilderness.net/index.cfm?fuse=NWPS&sec=stateView&state=mt

The following paragraph is from the National Forest Management Act. It states:

EVALUATION OF POTENTIAL WILDERNESS AREAS

Carefully evaluate potential wilderness areas to determine their suitability for inclusion in the National Wilderness Preservation System and to determine the mix of land uses that best meet public needs. An area recommended as suitable for potential wilderness must meet the tests of capability, availability, and need. In addition to the inherent wilderness quality it possesses, an area must provide opportunities and experiences that are dependent upon or enhanced by a wilderness environment. Also consider the ability of the Forest Service to manage the area as wilderness.

http://www.fs.fed.us/emc/nfma/includes/directives/fsh1909_12_chapter_70_wilderness_evaluation.pdf

Clearly there is no need for additional designated wilderness lands in Montana, nor any other western state for that matter.