With stock gearing in the 70-72 mph range.
Don't know of any KSX, but a KFX450 will run in the range of 75 - 79 mph in stock form.
About 70 to 75 mph
61 mph
A 2012 stock yfz 450 goes about 75 maybe 80 and the 2012 stock raptor 700 goes 75-80 The yfz would win in a race to full speed because is accelerates faster and it weighs less