Finally had the X74 installed on our '04 40th Anniversary. My wife and I did our normal 400 mile loop and here's some comments after 550 miles on the suspension. The drive consists of back roads through the center of Florida, highway and urban areas.
The best summary I can make is the car feels like it shed 300 pounds. For us, with the exception of ride height (which is more a function of the 996's front-end overhang than the ride height), this should be the stock 996 sport suspension.
Handling: Given that the limits of the car have increased to the point public roads can no longer surface any weaknesses, here's all I can say. Compared to the stock US sport suspension and alignment, the handling is vastly improved. Some noticeable changes: 1), the front end now feels like its part of the car. Fore and aft balance is much better. All floating is gone and at speeds up to 120 the car feels lighter but effortlessly glued to the road. 2), tracks and points much better. In curves there's no longer any waiting for the front-end to respond. 3), much more responsive to throttle, braking and throttle steering. 4), vastly improved composure in any curve we can find in Florida. 4), a much simpler car to drive. My wife said "less nervous and just feels like it knows exactly what you want it to do and does it". All nonessential body dynamics are gone. When you get on it or brake, the car responds, no lift, no hunkering down, it simply goes where you want it to go. On the highway its lovely: no float, tram-lining is way down, the car is no longer affected by side winds and there's no more constant attention to steering corrections. Champion did the install in their Motorsports group and bumped the tire pressures up to 35f/40r from our 32f/36r psi. At this point I'm in no mood to experiment.
Ride Quality: My wife says firmer but much better controlled. I say 95% of the time its less harsh (yes, less) that the stock suspension. There are absolutely no abrupt transitions or any feeling of the car being high strung. The control is smooth and any firmness is so well integrated its simply a joy to experience. The improved control and substantially reduced body dynamics make it a pleasure around town or on the highway. The bump stops do come sooner. I've intentionally bottomed it once on an abrupt bridge I know of. Its a harsh stop but so was stock. The car is at all times smooth and a pleasure to drive. We have no reservations about the X74's suitability for the street or any desire for improved ride characteristics. I have heard a comment about the X74 oscillating on certain road surfaces. This did happen once for maybe a half mile. Its subtle and a non-issue for me.
Ride height: After 550 miles, the car now sits at 25" front and 25.5" rear. That's a 1.1" drop at both ends. There was a GT3 sitting next to the car when I picked it up. Using a pack of cigarettes as a reference, the chin spoiler sits a tad lower than the GT3's spoiler. I expected problems. When bottoming the car nose down, no contact other than I could hear the rubber that sits behind the front tires rub a bit. Taken straight on, steep driveways are a problem. Using a little bit of common sense took care of this issue. Getting in and out of the car is the same. Looks was not one of my criteria. It was with Monica. Neither one of us can see any difference but the car now looks right. Having said that, the car feels and appears smaller. Combined with the lighter feel, this was an unexpected bonus.
Cost: Installed with an engine plate, $2,800. Given the results, the cost is irrelevant.
Source: Carnewal for parts, Champion Motorsports for the install. Both get nothing but high marks.