I have not backpacked in the Sierra, but from the descriptions it sounds warmer than the Winds. Certainly the weather in the high Rockies is definitely more severe and more apt to be below freezing than in the high Cascades of Washington and Oregon. In the Winds you can get snow and temps down to the mid-teens even in midsummer. Last summer it snowed almost a foot in Titcomb Basin on Aug. 8 and again on Aug. 15. At Elkhart Park the morning of August 9, the temp was 20 degrees, and that's just the trailhead. In the Winds, you can expect a daily round of thunderstorms starting mid-afternoon. I don't believe that's true in the Sierra; I know it's not true for the Cascades.

Hopefully Wandering_Daisy, who is very familiar with both places, will chime in!