Ok this may sound silly but when you changed your pads did your pistons push back nice and easy cos I went o the flig we the boys on hear and upgraded the brakes to 4pots for better brakeing lol and found when above 45 got a judder thrue the steering wheel and when higher up the speed got worse so Thot discs the pads wer needing done so fitter ebc red stuff pads and that's when I found a sticky piston had a wee bit of rust on it gave it a clean we emery paper fine grit clarted on the copper grease then tryed agen went back so smooth and with little pressure on ma leaver
Hope that helps and if not hope you get to the bottom of it