And I trust you didn't actually exchange the Speed enhancement for some other enhancement. You simply removed it. In that case you are comparing two styles with one using a much weaker weapon -- Speed is a hefty +3 enhancement bonus after all.
I did make an additional check at a lower level without a Greatsword of Speed. In that case TWF damage was higher, but again, not by a lot. Nothing to be excited about, since the style requires a feat to use and using a Greatsword does not.