I don't know if it will be the same for the Mustang, but on my GTI I have Koni STrt shocks and they certainly are not OEM+, they are about as stiff as the Koni yellows on the 3rd click up from the softest, they make for a rough ride combined with stiffer springs like the H&R race springs I run. As far as how they have held up they have been on there for about and year including one Upstate New York winter and they still perform the same, They have begun to make a squeaking noise over harsh bumps and I've noticed a little seepage at the top but the housings have next to no rust, no complaints.
Owner reviews for shock absorbers
I bought my 2003 with some autostore garbage in the front (Monroe or Gabriel or some such crap - don't remember now) and the rather tired OE Sachs/Boge in the back. The damned thing was scary do drive above 35. Installed Bilstein HD 24-019118 ($203.90 for the pair from eshocks) in the front and the 24-214230 ($185.50 for the pair from eshocks) in the back. Very happy with the result. Took the bus above 100 in Texas and Arizona on the way to California this past January - and what a difference this made! It sat on the road like a flatiron on the ironing board. Also, do keep in mind that Bilstein shocks carry lifetime warranty and the company stands behind it 100%. My S6 currently rides on its 3rd set of Bilstein Sport (after 2 free warranty replacements) in the 16 years under my ownership - Bilstein replaced them each time w/o a flinch. Konis are good, but they sometimes leak. Bilsteins wear out but they don't leak. At least in my experience.
I have a 1993 GL with Bilstein HDs. They are firm but I would not want them firmer. On a heavier VR6 camper I would think they'd be even more suitable for the job.
I have installed the shocks/springs for month and have decided to sell the vehicle due to new family member arriving soon. These transformed the car. Really nice set up. Smooth ride and handles really nice. Sticks to the highway very well.
I had FSD's with VWR springs on my 12 R and it was an excellent combination. Granted that was one of the worst riding cars I've ever owned stock, so the improvement was very noticeable. It handed better as well.
My Corrado has Koni yellow shocks at stock height and the rebound/stiffness is set right in the middle. It's a pain to adjust the rear stiffness, but somebody sells low profile knobs for them. The car is in storage so I don't remember if the rear spring perches are adjustable. I do remember that the car rides great and I can just adjust the stiffness in a few minutes (on the front anyway) if I want to corner flatter.
I bought a set of adjustable koni yellows with vogtland springs for my jetta for $40. No idea how old they are, but throw on the stiff setting and they rock corners pretty well.
Bilstein does make an easily-obtained, affordable, heavy-duty shock absorber (front and rear) that's a direct bolt-up option for these cars. It's what I swear by.
I then went with WRD sport springs and Koni ST.R shocks/struts with a eibach 25mm rear sway bar. It was much softer and I enjoyed it but it has more body roll than I want and the Koni's seem to be too soft for what I want, so I am going to change it again.
The Koni STR.Ts I have started to rust at about one year old. It seems to happen a lot on them according to TDI club.
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