My other source for track days is www.lotus-on-track.com
They are very friendly AND professionnal, accept very nicelly other cars than Lotuses (I used to have one and will discover how it is with the M3)
Otherwise, the new www.belgiansontrack.be
seems promising but not yet tried. Abbeville is fun with small and light car but too short for BMW,Porsche,...
Will let you know.