US 2 profile and weatherI90 profile and weatherThese 2 pages give an idea of how the 2 routes compare, though they aren't drawn to scale. With both the climb up the east side is more gradual. US2 descends quickly on the west side to a river valley, though I don't think the grade exceeds 6-7%.
You can also drive to Wenatchee via I90, Quincy, WA28. I think it's a toss up as to whether that is better than US2 all the way across the flat interior. Both have to drop to Columbia River level. WA28 might be more gentle than US2.
After visiting Cashmere, you could continue on US2, or take US97 (and WA197) to I90. US97 has Blewett Pass. (Leavenworth on US2 is another interesting tourist stop.)
And advantage to taking US97 is that you could head to the south Sound via WA18, bypassing I405 through Bellevue and east side.
traffic and webcams for Seattle Note the links to maps for adjacent areas. There is road widening and blasting on both I90 and WA522, but they try to time that to minimize disruptions.
Close to McChord I'd stay on WA167 and 512 through Puyallup, avoiding potentially slow traffic through Tacoma.