Should be the same. Could be that your eyes are playing tricks on you, with the glacius being a rather thick sword, compared to the katana-like acheron.
There are many ways to measure the speed of a sword. One of them is combos per minute (CPM). The guild Lancer Knightz has been collecting data on CPM on various swords. Acheron and Glacius come out the same in CPM.
Should be the same. Could be that your eyes are playing tricks on you, with the glacius being a rather thick sword, compared to the katana-like acheron.