Boost of Movement only grant +97 MS but say they grant +105

This is because MS has a soft cap here, unlike in DOTA/HoN. In both of those games, you can get a max of 522MS(Someone feel free to correct me on that) whereas in LoL MS items/abilities grant less and less the higher you get.

I believe the soft cap is (something along the lines of) %80 times any bonus ms past 410, and %50 times any bonus ms past 500. Those probably aren't exactly the right numbers, but they're pretty close.