So according to this:
http://www.hcsharp.com/tesla/roadsterAlignSpecs/AlignSpecs.htm
1mm should be around 0.25°
Mine are:
Front Left -0.30° - Front Right is perfect
Back Left -2.30° - Back Right -2.06°
So I should need 18mm in Total. Quite a lot!
The Opel Speedster should use the same parts, and they sell 1mm and 3mm ones, so I will probably get them there.
Thanks for all the tips!