To answer (or perhaps speculate) some of the questions:

I believe that GP7 1617 is being acquired by EWG to operate the Geiger Spur

Nothing has been done in the way of refurbishing the remaining Geiger Spur track. I believe that this is planned for a future project. I do not know the timetable. The next phase, scheduled for spring/summer 2009 will be removal of the track across Fairchild AFB.

I do not know why 20 mph was chosen for the newly constructed trackage. Time will tell whether harmonic rocking will be a problem. I would think that several factors might combine to reduce or eliminate the harmonic rocking tendency. The 115# Rail lengths of 78 feet and 6-bolt angle bars and concrete ties should provide a very rigid track structure. Rocking usually is accompanied with a lot of up and down movement in the rail joints. The good subgrade and heavy ballast will also help. The steel beams handled on bulkhead flats or gondolas may have a lower center of gravity than grain cars. This should help reduce rocking. The relatively short trains also should reduce the rocking tendency.

The wildest rocking I have ever seen was several years ago on UP's former SI line in Spokane Valley. This was before they did some tie work and field welded the track joints. Some of the joints would flex 2-3 INCHES up and down! At times I wondered how they stayed on the tracks. A few times we actually saw daylight between the rail head and the wheel tread.