Hi sje00,
Based on my experience of my 996 C2, and hearing stories from others such as DynoMike, I'd say that the 996 is very sensitive to what I assumed were small adjustments in geometry.
I first tried a Factory adjustment for X74 (My car is on H&R lowering springs which decrease ride height by 30mm all round) but with more front neg. camber. Which was 50' neg Camber at the front and 1 deg 40' rear. The toe was standard, so 5 ' toe in front and 10' toe in rear.
The car felt good, and when really laying power down after the apex of a corner, I could feel the car going from a slightly understeer to oversteer balance which feels really nice.
However I felt that it was slightly slow to turn in, and the car was a bit too "stable and steady" for my liking, also, the inside edges of the rear tyres were wearing fast.
Second try, working with 9Excellence in Horley, I discussed with them what I'd like to try.
I've gone with the maximum neg camber I could achieve on the front using the slotted top mount holes and standard control arms my car is fitted with.
Front is now 1 deg 22' neg Camber. Rear is 1 deg 20' neg Camber. 9E advised that they wouldn't put less neg camber on the rear. The toe angles are as before....
The car is Soooo much more pointy and eager to turn in. I like this, and the car as a whole feels smaller and more agile on the road. Rear tyre wear is improved, but I feels I may have lost a little of the under to oversteer balance that I enjoyed before, so may eventually dial a bit more rear neg camber back in..... say 1 deg 30'?
The point I think is that:
1.) The car, if all the suspension is in good nick (I've replaced pretty much everything) appear very sensitive to small adjustments.
2.) I think that (as ELA has found as well) more Front neg camber is a lovely thing, but individual drivers will have distinct preferences and not all agree
3.) My car is only used on the road. Track settings will be different again
4.) Using a good specialist such as Centre Gravity, if you can get there will be a good idea, and ultimately save you money in the long run I reckon. However, there are lots of other good independent specialists that will do a good job based on their experiences too.
Good luck