When I testdrove RUF's 996 Turbo R prototype a while ago, it had the OEM suspension on it, no mods at all. When I asked Alois Ruf about a possible suspension upgrade, he said that the OEM suspension setup is very good (no doubt about it, I can confirm that) and it is difficult to find a better setup. After the ride with the prototype, I didn't drive a RUF 996 Turbo R anymore.
Regarding the H&R suspension: there are different versions of it. I testdrove two of them, the street version with double springs and the racing version with double springs. As far as I know, there is a third version without double springs but a very good setup for racing.
The street version is very balanced, still some mild understeer present but cornering is much more precise and stiffness is not more annoying (or not) as on the OEM setup. I'd recommend different swaybars with this setup if you want to seriously track race this car. Lowering on the car I testdrove was about 30 mm lower than OEM ROW setup. That means even 10 mm lower than the OEM GT2 setup. I guess lowering the TT further could induce some serious problems on the street (ramps, etc.).
The so called racing version of the H&R coilover kit I drove was very stiff, even a bit too stiff for street driving. Cornering felt not much different than with the street version but I wasn't able to push it to the max because I testdrove it on a public street. However the steering felt a little bit more "nervous", especially at higher speeds. The directness of steering-in was better but also with a narrower margin than with the OEM or street version of the H&R coilover kit. The car I testdrove had different swaybars too and it felt very good balanced. No understeer at all with a mild tendency to oversteer, especially because this car was equipped with a 543 HP power upgrade.
Overall I made my own conclusion: if I want to drive my Turbo mainly on the street, I'd go for the street version of the H&R coilover kit and maybe add some swaybars to it.
For mainly track driving, I'd go for a H&R coilover kit incl. different droplinks and different swaybars too.
It is very difficult to give you an advise which setup would be best or the fastest. The problem is that in fact you have to adapt the suspension setup to the track you're driving on. What can be fast on track XYZ, does't necessarily have to be fast on track ZYX. The Nuerburgring Nordschleife is a pretty good example for that rule: people who install super stiff and low racing suspensions on their cars are very surprised that they're slower than other cars, even with OEM (!) manufacturer setup.
Stiff and low is not always the way to go.
I hope I could help a bit, sorry I can't explain it better in my bad English.
BTW: the best "overall" setup proves to be the OEM ROW setup. But many people laugh at me when I tell them.