Michael,
There is the slightest drag at roughly a 100 kph, but I have to say that I'm rather pleased with how the car behaves now. I feel I can trust it a whole lot more now than before.
The type of tyre and condition / age of the tyre and condition of the road you drive on are definitely all very important factors in how the car behaves. I have driven 31 with:
Antique Michelin X's, Dunlop Racing, Excelsior Racing (Cross ply), Excelsior Radial and modern Michelin X's, all 5.50 x 16.
What I find intriguing is that straight line stability was possibly better with the 20 year old Michelin's than the new X’s, grip is something else though!
Jonas