An estimate of Sion's damage potential
Here is an estimate of what Sion's ult can do in real life:
Math has been left out because I already had to remake this post once, and I'm too lazy to do it all again.
* Sion's base speed is 2.76 m/s
* Sion's max ult speed is 7.6 m/s (27.36 km/h or almost exactly 17 mph)
* Assuming constant acceleration to max speed over 4 seconds, Sion will travel 51.12 meters during his ult (if uninterrupted)
* If Sion were to compete in the 100 meter dash, he would finish in 14.43 seconds (an average time for an adult male is 15-20 seconds - without armor and weapons, and having two good feet)
Now, for the real meat:
* Based on some research around heavyweight boxers (seems appropriate to find Sion-like individuals), an appropriate weight for Sion (without armor) can be estimated around 110 kg (just over 240 lbs)
* His armor is not a full suit, but is considerably thicker than that of a normal medieval knight's. Add in his metal boot/stub and his soul furnace, and we can assume his armor weighs roughly the same as a knight's - about 20 kg or 45 lbs.
* His axe is ridiculously large. The largest I could find with a weight had a head of 1.5 ft across weighing 10 lbs. Tiny. Based on the size of Sion's axe, I will assume it weighs approximately the same as his armor.
* Therefore, Sion's total weight with armor is estimated as 150 kg or 330 lbs
* We can now calculate the force of impact from Sion's full speed ult (estimating a 0.2 second stopping time) as 5700 Newtons. This would feel as though something weighing 581 kg (1281 lbs) was sitting on you.
Conclusion: Ouch.