I do a lot of trackdays on my (07) SD, Kyalami (wsbk) and Phakisa (old motogp track); bike is quite frankly brilliant, and punches waaay above its division. My friend (05 SD) and I did 2 2-day events at Phakisa mid-08, and they still talk about 'those crazy ktm dudes'.
I test-rode a 990SM about 3 months ago; I didn't find any benefits over the SD; the power was down, felt heavier, and the front didn't feel as.... secure as the SD. Coming from superbikes to the SD, the SM was a step too far seating-wise for me, and just felt odd.
The only thing I crave is a bit more power. But then, I'm in South Africa, where the roads are mostly straight. And I came off a 154rwhp blade.