The warp calculation was changed after TNG. Tom Paris went Warp 10 in a VOY episode, which was considered the speed at which you are everywhere in the universe at the same time (any faster meant time travel). But by pre-TNG standards, this is nothing. There was a ship in the animated series that went at Warp 36, but again, the calculation they used back then was different.
According to Star Trek Online Federation transwarp technology brings ships up to Warp 20 in the year 2409.
According to Star Trek Online again Borg transwarp technology brings ships up to Warp 14 in the year 2409.