while i did my best to eliminate or prevent as much geometry change thru the suspension cycle, when you have 18" of shock stroke, you will experience some axle rotation, it's a fact. On the street, given that i don't run swaybars right now, i cycle the suspension about 4-5 inches per side based on regular around town driving.
if i were to really reef on it, i could make some passengers soil the seats, but that's more a testiment to how soft my airshox are at their current setting than problems with my geometry.
My focus was on CASTER, and bumpsteer, as i've long been a proponent of the A arm style of geometry mainenance. On trail runs where there's agressive cycling and twist of the axle in articulation , i notice only a slight bit of rear steer from the aft system. I would atribute that to the shorter links in the rear than the front. My rear is presently the |\/| style. over the winter i'm going to experiment with a /\/\ style of rear system to correct that.
As for the need of a panhard bar, i don't feel the need for one yet, an in fact i've theorized that one might actually bind up my setup on straight up and down travel due to the radial arc laterally that the bar would introduce. the 4 link system is intended to be without lateral shift on true up and down style of cycling. Articulation would not be affected by the panhard bar IMO.
with the lenght of the arms, triangulation that i've used, and the Johnny joints, i feel that a hydro assist is manditory. when i had the ram off for re-location , i had some instances of deathwobble over washboard on the street doing exactly 30 - 33 mph range. strange harmonics i guess. going faster or slower: wouldn't happen. now with the hydro over the same section, same speed; no wobble. I've added some extra caster to make sure too.
One thing to consider with leafs is that in a fron suspension setup, the section of leaf from the fixed hangar and axle is in essense a "link" and the forward section to the shackle is mostly part of the "spring" equation. Now it is also true that the leaf locates the axle laterally which is why the talk of the panhard or track bar comes into the situation. as the rear bushing wears, it allows a point for slop, inducing wobble.
my $0.02
