Turbo S is the same as a normal turbo with X50 and ceramics.
As long as both cars are standard, then GT2 should be faster. The suspension is 20mm lower, harder, with dual rate springs, and different damping. All suspension is metal jointed for better wheel location.
GT2 weighs less, due to no 4wd system and other small weight savings, about 100Kg I think, and has about 25 bhp more (although there were two versions, the last ones had a bit more ooph).
GT2 is rear wheel drive, with no PSM. So, with non-linear power delivery, you need to know what you are doing, especially in the wet.
In poor conditions the turbo could beat a GT2.
If the road was very rough, the softer turbo suspension could also help.
GT2 could come in comfort or clubsport spec. If you were going to get one instead of a turbo, then I saw no reason not to have the CS.
In a straight line, the extra acceleration is noticeable, but not that massive. The GT2 will edge ahead. I don't know how much but a car length or two by 100 would seem reasonable.
Handling is better on a circuit, but it would be hard to quantify. In any case it is more largely affected by confidence and driving ability.
GT2 is harder to drive than a GT3.
However, if you were expert in both, then the GT2 should be quicker. But it will depend on the circuit.
A tight twisty little b'stard would favour the 3, due to higher corner speed, lower weight and smoother power delivery (say like Monaco). But a good GT circuit, like perhaps Le Mans, would favour the 2.
2 has a higher top speed and more acceleration, if you can use them.
If you modify both of them, then the 3 gets a bit more power and better handling, but the 2 can just have silly amounts of power.
650bhp+ (RUF or 9ff) and over 220mph top speed will beat the 3 with a few of Manthey bits on most circuits, if you can control it.
TTS was around 101K and last GT2 were about 135K I think.
More interesting is whether a 993 GT2 is better than a 996 GT2? Aside from the depreciation stakes that is.
Migration info. Legacy thread was 95387