Finally had the mufflers replaced with two Simons Heavy ones (500 x 220 x 140mm) and dumped the 100mm end piece and just put a 2.5" pipe at the end. It now sounds great, no drone on the highway and a very polite purr untill I put my foot down. The center muffler is a tad too wide so it's hanging a bit low but it'll do for now. Also had my first track day and everything survived. Unplugged the brown temp sensor so the fans were constantly on, thermostat took care of the rest and temps remained steady at 90 degrees once the engine was warmed up. Did a few 0-100kph sprints on my daily tires and managed to get 6.4 seconds so 1.5 seconds quicker. I have a feeling I should be able to do better but I'm wondering if that's because of the driver or maybe some suboptimal parts. Considering a fermer rear end next. Or a lightened flywheel. Or probably both :-)