The lowrance ghost is quite a bit faster then a Ultrex. The garmin is even faster, its the fastest trolling motor on the market right now, My buddy is getting 3.8mph on his 21XB alli only on 24V.
Also the garmin and lowrance will use less battery power. When i switched to a lowrance i noticed about 20% more battery life sometimes more depending on how hard i was on it, but on avg 20% more