Yes, the rear-engined nature of the 911 series induces a steering feel that is different from any other car I've driving. You can 'feel' every small rock, pebble, change in the road surface (good), but the wheels are 'light' over the surface. In a much more grown-up way, the 911 feels like my racing kart in a previous life in which the front wheels just bounce and skid over the surface and you are guiding a missile rather than the tread being really planted. All a taste issue, and something that is a very effective design once used to it.
That all said, no one has mentioned (in addition to the camber setting - which I agree needs to be checked) the 'rake' (front to back angle) after the lowering. I wonder whether an altered rake angle plus the state of the splitter is letting too much air under the car at speed. You will definitely have issues at high speed if you're not properly shoveling air over the car.
BTW, if you have a chance to borrow (dealer or friend) another 911 to take out on the same course, you'll be able to see if it's 'you' or the car. Worth doing before you pursue too many options.
GL

 

I have HR springs mounted and the HR sways still in the box. It will be mounted tomorrow. For the sways i'm thinking to set it soft at front and neutral at rear and as sways don't change the wheel alignment, what do you think of my current wheel alignment:

_________________FL__________FR
Camber...............-0º50'..........-0º50'
Caster..................8º01'...........7º51'
Toe.....................0º01'...........0º01'
SAI....................18º45'.........17º40'
Included angle.....17º54'.........16º50'

Cross Camber.........-0º01'
Cross Caster............0º11'
Cross SAI................1º05'
Total Toe................0º01'

_________________RL__________RR
Camber...............-1º37'..........-1º41'
Toe.....................0º10'............0º11'

Cross Camber.........0º04'
Total Toe..............0º21'
Thrust Angle..........0º00'

 

The light feeling at the front from a 25mph headwind could be expected if your ride height front to back wasn't 1 degree nose-down.

I found once I had the correct ride heights (-15mm front and back making 117/138mm) that the front weight was much better at faster speeds ie. the car was nose down and so I got more downforce on the front.

I have posted before others alignment settings:

 

After doing some research and comparing that charter with my values, i think that i may conclude that:
Front: a bit positive toe (0º01'), more stable for high speeds but less responsive; less agressive camber (-0º50') than most, i have to check how the tires is wearing to see if it need more negative camber; caster (8º00') is the most positive as possible for a heavier front feel.
Rear: it share the same toe (0º10') than most of that charter, the higher recommended by porsche for our cars and even GT3 and GT2 can have only a bit more posive toe (+0º03'); the rear camber (-1º40') is here we find more difference, i have the most agressive setting recommended by porsche, have to see how it wears.