In the Star Trek: The Animated Series episode, "The Counter-Clock Incident", the Enterprise is on an assignment to facilitate one of the earliest captains of the Enterprise, who'd reached involuntary retirement age. On the way, they pass through a nebula which looks beautiful on the outside but is extremely deadly if ventured near to.
Suddenly, they see a ship approaching, which is seemingly at warp 45. They try to slow it down with their tractor beam, which has hardly any effect on the renegade ship, but increases their own speed to warp 44 or so. (The rest of the episode, where they go into a backward universe to Karli's (the ship's captain) home planet "Arret", which I am guessing is backwards for Terra, is not of much importance here).
The real question is, when Janeway and her team achieved warp 10 in the Voyager episode, "Threshold", they turned into sloths, while these guys didn't even when going to four times that speed. Is this just a direction issue or something else?