Used eibach lowering kit on my turbos !
Looks very great with zero issues ! Dealer shop did the installation !

 

I've installed the GMG springs and am very happy with the improvement in stance as well as the ride quality, especially in normal mode. From my experience the springs impact the rebound rate over bumps and the leaning or listing during turns but it is the shocks that really define the stiffness.

This becomes evident in sports mode because even with the GMG springs the stock shocks are so stiff in sports mode that they dominate the overall experience.

To put it another way, aftermarket springs like GMG, H&R or eibach should all improve the ride quality in normal mode by eliminating the "bobbing" sensation from the mushy stock springs, but in sports mode the ride feel is dominated by the stiff stock shocks and you won't notice a huge difference over the stock springs

Either way get some aftermarket springs if for no other reason than to lower the car, stock ride height is for SUVs

Hope this helps
Art

 

Art, this is an excellent analysis and in a few sentences you've actually given me a very very good "glimpse" into the GMG spring's behavior.
I would like to add the following: true, the shock would define the stiffness, but only if you let it to. Both springs and dampening force define stiffness. In other words,

If a is spring rate, b is dampening force, then, as a gross simplification:
a + b = "stiffness"
If either a or b is off the chart, in this case b (the flaw design of Sport mode in PASM gen 1), there is nothing you could do with the spring to reduce the stiffness.
The only way to truly get rid of the problem with PASM gen 1 is of course to switch to a coilover.
In the stock shock, the damping force is set (seemingly) at 1 for Normal mode, and 10 for Sport mode (making this mode mostly un-useable).
In Bilstein Damptronic shock, the damping force is set more like 4-5 for normal mode, and 6-7 for Sport mode. (This is why people new to the Damptronic sometimes think there is no difference between the 2 modes. There is.)

BTW, a couple things for OP to consider: GMG and Techart springs are stiffer than stock, whereas H&R's ride very similar to stock. If you are looking to stiffen the chassis, GMG and Techart are good choices, and H&R would become stiffer only if you add other components to stiffen the system such as sway bar, drop link, etc.
Another point to consider is that all lowering springs drop the ride height a fixed 1 inch, whereas coilover drop is adjustable (I would recommend only 10-15mm so there is not too much change to the suspension 3D geometry.).

 

^^^^^ cannga. Good clarification as my comments were specific to the combination of aftermarket springs with stock shocks in sports mode.

At the end of the day aftermarket springs are likely not going to "soften" the feel of the ride in a 997.1 TT in sports mode as the stiffness of this setting is a 10 out of 10 and requires different shocks to modify the ride feel

However with that in mind the GMG springs are excellent if you want to lower the ride and improve the feel and handling in normal non-sports mode while not messing with the rest of the suspension

Art

 

That's s great deal! I'm calling them in Monday!

 

H&R works for me

 

H & R here. Great stance and stock like driveabilty

 

STILL way too high!!

 

It's high but they give you warranty!

 

H&R here. Handling improved, ride quality didn't change. The flaps on the front wheel liners scraped over bumps so I cut them off. Car feels great:

 

+1 for GMG springs, do their sways at the same time!

 

Just got my car back from EVOMS lowered, sways, and aligned. I posted some pics - same link as post #2