I agree the ride on my 700 can be 'rough' at times, especially after the fully suspended Quest.  But, I don't change tires and all that like some.  I ride the skinny's all the time.  The one thing is after the Quest: I 'feel' faster...might just be that I can see the ground again, or the rough feel of the road.  But they're both great for me!

The previous owner put 35s all around on my 700.  Since I have not ridden with the skinnies I can not say more soft or not.  I will say it is still a bit jarring on rough sections.  I will also say I am definitely slower on the trike than on my high racer but some of that is due to a lower level of training this year.  As for the next level trike the 559 might be an option although it sits higher than the expedition but the seat recline is also adjustable.  I do not remember if it will match the expedition on recline.

You could always consider an ICE Sprint 26 with full suspension. Put the skinniest, highest pressure tires on it that will fit and let the suspension smooth out the ride while you fly.

Took the 700 out to the GDB Mesquite ride last night...  The "fast" group tends to roll at 18-22 mph, similiar to the Airport ride, but Mesquite has got more hills to climb, and almost no stoplights -- so this was ~16 miles of nonstop keeping up, out to the 7-11 on Cartwright.
 
Frankly, this is the hardest I've worked on the Mesquite ride in a LONG time -- it felt more like a 16 mile time trial!  But, I kept up...
 
Observations --  
 
1) the 700 coasts downhill at essentially the same speed at the DF riders do -- so the three wheels and perhaps additional wind resistance definitely make it slower than the Xstream in that regard...  I easily outcoast the others when on the Xstream. However, I hit 37mph on the Barnes Bridge downhill, and the steering was rock solid.
 
2) When putting power to the pedals during hill climbing, sitting up in a "crunch" position greatly reduces the pedal steer effect.
 
3) Again, I had essentially no mental concerns about road hazards causing a wreck.
 
4) Riding the 700 in a group gives me an excellent view of DF riders' calves  
 
By the time we got to the 7-11, I was tired -- the ride back was at a more casual pace.
 
Here is the route, and speed/elevation tracking for the segment out to the 7-11:
 

 

 
Compare that elevation map to that of the Airport Ride -- you'll also notice many more stoplight stops on the Airport Ride.
 

 
It was an interesting challenge, keeping up with the group -- I doubt I would have been able to, on a slower machine.

Paul, I don't get a "pedal, steer effect" on my 700. I have never had to crunch up to put power to the pedals. Maybe it's the ultra skinny front tires or something slightly out of adjustment on that trike. Of course, I use the big ring and shift down in the back if necessary when climbing easy hills. I use the middle ring on steeper hills. That may be the difference on my trike.
 
I have often wished to try the trike on that ride but was certain I wouldn't be able to keep up on the climbs. Seeing that you had to employ your best effort, I now know it would not go well for me.

Figured if I responded and pointed a finger at a potential trike issue, Mr Wizard would respond  
Really didn't think there could be an alignment issue or any deviation given that it is Mr Wizard's trike so I agree there's only one possibility remaining - the engine!

Doug, you and Daniel are very experienced cyclists.  When I loaned Daniel my 700 last year (yes, I'm the guilty one) I commented at the start that the pedal steer would go away with practice.  By five miles into the ride, I was following him up a hill and watching him: no pedal steer.  What took me months to tame took him a couple of miles.  I also noticed no sign of the rear flexibility Bob Wand complained about with Daniel's new 700.  So it's apparent to me it's all about technique.  Paul, being in test mode, hasn't concentrated on technique yet.  If he starts spending time on a fast tadpole, he'll figure it out.