I had the rear header and deflector shields fitted, about £100 for the lot, (politely) haggle for some discount as you are having to pay to fix a design flaw ;-)
Makes a big difference, but don't forget you still have a Twin, which means the rear cylinder is located at the rear, in some ways better than all the four cylinder bikes I had that just blew heat right at the front of my legs on hot days, easier to move away from the KTM heat a little.
I suspect a "Hilltop job" would possibly help by reducing the piss weak Euro-4 compliant running conditions - or go all the way and fit a full system, a lot of heat is being generated and distributed by the Cat, removing that (and getting it properly remapped) is likely to have a very big effect, but I was happy to stop at around £100 rather than spend another £500 - £100 on exhaust and re-maps.