I've done everything you did in terms of carb jetting, except that i'm 2 and a half turns out, but i'm running the stock supercrapp with 12 discs. My best guess is that your supermoto exhaust is causing your bike to run lean. The fact your bike heats up a lot faster jives with the hotter, leaner exhaust gasses. I'd suggest dropping the needle back to the 3rd slot to richen it up and see if that helps.
If not, send your supermoto exhaust to me and i'll do a test ride to figure it out