^****. Do they really? I just ordered some Ikeya Formula front uppers. (i know not tubular, but they seem pretty thick)
anyway, i've got the PBM coils and i really like them. They are 18kg/mm & 14kg/mm front and rear respectively. I really like them, they are super comfy and go as low as you'd want them to. I've lowered them until the front upper control arms rest on the chassis, and I'm pretty certain they'll lower your car as much as you have in your sig pic. (I've since raised them to achieve the desired wheel fitment) Those spring rates may not sound super comfy, but i'm coming from an s14 that weighs 1000lbs less and a kidney bruising ride.I like the feel of the coils with the damping set at maximum.
Please keep the following in mind: I got these because they're local to me and i'm a loyal customer in the S-chassis crowd (since 06). They make solid parts and back them well. These are the only coils i've had for this car and I have nothing other than stock to compare them to.
Ultimately, they do what I want them to; provide awesome/comfy ride whilst dragging the chassis of our giant boats on the floor.
Yeah my friend has them on his GS, and the ride is amazing, I was more worried on how low they go, lol. Spring rates don't bother me I know how spring rates work to an extent, but I do know of people who think spring rates are the same throughout whatever chassis not taking in account of the vehicle weight.
^from that picture, it looks like the control arm is interfering with the chassis, and not the coilover top hat.
I've already notched there and cut a clearance hole in the engine bay to accommodate the control arm motion.
As for spring rates, yes, it depends on the geometry of the vehicle (motion ratios and moment arms). My s14 has 10/8s and feels way more stiff than the gs. (In fact, i'm going to order stiffer springs)
I dont think you'll have to worry about the ride height as a limitation. (Especially because of the large motion ratio).