I saw the low COG thread but theres like ZERO flex on most of those vehicles. I guess I'll settle for 31s.
i'm not a preacher for flex. but there are many more things i want in a suspension than max flex. with that said I still had more impressive flex than most rigs running similar sized tires on taller lifts. If you wan't to put larger tires on a low lift, you will have to tune your suspension to benefit you with a low lift to get the best results. Tuning means selecting components that will allow your suspension to perform to it's potential.
If you want flex with a "low cog" rig, look into things like running longer than reccomended shocks, if you are going to be bumpstopping to keep the springs from overcompressing and to keep the tires out of the fenders anyway, you can get a decent amount more shock length which in many cases is the limiting factor in most suspension setups. longer brake hoses won't hurt anything either way. Look into notching your shock mounts to clear the lower control arms on the axle better, or even look into running a longarm suspension.
If you want more flex in back some things to remember are; flat leaf springs allow the most flex. To get the most out of a leaf sprung suspension a good shackle angle is key, as is a shackle that allows your leaf springs to easily move (longer than stock)
On each end of the spectrum, bumpstops are key. As most know they keep your springs from prematurely sagging, keep your shocks happy, and keeps your tires out of your fenders. What is overlooked is the flex benefits that come with running extended bumpstops. Think of your axle as a see-saw, the bumpstop as the pivot point and each tire as one of the "riders", when the suspension is compressed to the pivot point yet the "rider" keeps going up, the other side is forced down to some degree. if you have a easily moving-bind free suspension, the other side will travel very far, if you do not however, you won't see as great results.
4" and 35's
1200 rti score (which is extremely well for a coil/leaf rig as i am told)
here is a 3" lift and large 36's