I can vouch for the JTS anti-tramp springs in a race car - they communicate very well with great feedback in more extreme conditions than normal road use. I would perservere with your springs in the meantime and investigate those Bilsteins - it sounds as though they may be incorrectly damped for your car. Also you should acknowledge that running 140kph through a public road corner is probably on the limit of a 1200's handling and a driver's good sense.