I'm on a road trip. The Michelin Pilot Sports are on. New wrinkle: the OE GT rims are not on my car. These TSW "Watkins" rims weigh 13 and 14 lbs less than the OE GT rims do. To what extent this contributes to the handling I am enjoying - and how much of the increase in cornering prowess is me just slowly getting used to my car - I am not able to say.
I can positively say that all the "up and down" sections of the highways (and there are plenty) are only the road, not the car bouncing along with them. The Eibach on "soft" is solid. The road drops or rises and the car does also, without subsequent movement in the vertical. Cornering is really good. I am more daring than I was during the winter on the Nitto Motivo A/S UHP tires and the GT rims.
Unfortunately, my scheduled drives during the week changed and I hardly ever get over to "my skid pad" and high speed interchange (see above). So I don't have an update on how the Pilot Sport tires and the rear sway bar compare in the "Gs" department. I'm going to have to dedicate a spot of time to that and just go do it a few times. Later ...
Keep us posted, looking to hear some more on this. I’ll be getting mine installed once I get back stateside. Been missing my ride and I haven’t seen one in the Philippines, HK or Singapore in the couple of weeks I’ve been here.
So, I have determined that my present setup is better by far than Nitto Motivo UHP A/S on the OE GT rims, as far as "spirited" cornering goes.
Here's the recap: Several months ago I tried to corner on the cloverleaf (skid pad

) as hard as I could manage, with the above setup: I was curious to test the Motivos against the Pilot Sport 4s. The G meter showed .6 G, then .7 G started the tire noise, and stabs of understeer occurred as I tried to push .8 G. I couldn't hold .8 G.
Since then, I have put the Eibach rear sway in (soft setting); put the Pilot Sports on much lighter rims (TSW "Watkins", weighing 13 and 14 lbs less than the OE GT rims), and wider rims to boot; they are a full inch wider than the GT rims; resulting in stretched sidewalls i.e. stiffer sidewalls resulting in the rubber patch being more planted (so logic says, and so I am told). Today, with this setup, I took the "skid pad" (cloverleaf) onto I-15 northbound from I-215 eastbound, and despite my rather inexpert cornering in the sustained (270 degrees) curve, I was easily able to hold .7 G, and finally near the top, .8 G according to the G meter. I would have powered out of the top of the cloverleaf, beginning with .8 G, but I came up on the exhaust pipe of a motorcycle which was nibbling on the bumper of a vehicle in front of it.
So, .8 G for sure, with Pilot Sport 4s, on rims an inch wider than OE GT rims (and 13, 14 lbs lighter), with an Eibach rear sway bar: and no tire noise, no understeer. I think I can push this to .9 G and hold it, and then power out from there at the top. We'll see!
What part of this is the most dynamic? Is it mostly tires? (I'd say yes to that) Followed by the upgraded, aftermarket (much lighter and a bit wider) rims? The Eibach sway bar improves the feel of the cornering, but does it make it faster? I don't think so, but what do I know?
(One other factor going forward: the Wheel Werks guy said that if I had fresher rear tires I'd be able to corner even more aggressively. Right now, my Pilot Sport 4 rears are at 3mm in the center and 4 or 5mm on the edges, while the front tires are 6mm across the tread. This worn rear tread condition means that holding .8 G is likely to change for the better when I get new treads on the rear in another one or two thousand miles.)