Springs...
I ran an 11 SB Assault last year, and my spec sheet said the same. I went ahead and ordered it to put on. I am from northern iowa, and didnt want to have problems on my short trips out west. I will say the sled ran flawlessly. Never missed a beat and held 8150-8200 rpms all week. I would say for the price of the spring, Get it. Just to be safe. I never ran the stock black spring out there so i guess i dont know how well it wouldve worked. But i wouldnt want to lose a day messing with changing out clutching when i could be riding... Thas my opinion anyway.