Here is a look at the profile of a Sierra Cascades segment. I took the lat-long-elevation data from a GMaps route run through GPSVisualizer to get the GPX. The distance and elevation difference has been computed between each data triplet (more than 8,000) and the result displayed below. (Elevation in blue, gradient in red),



Similar procedure for a segment of Eurovelo 6 (but legend is reversed -- elevation in red and gradient in blue)



I've analyzed a couple of hilly courses with which I am familiar. Too early to tell for certain, but as of now my impression is that sustained gradients above 10% with a fully loaded touring bike exceeds our curent capabilities, so it looks like we'll ride EV6 next Summer after all