I think there supposed trip to infinite velocity wasn't figured out 3-dimensionally. These inventions they are using; warp theory, centrific dampeners, hollowdecks,--- are speculation theory that must be tested and re-tested over and over again and then re-wroked so the theory and machinery is useable. Roddenberry, Bragga and the writers are frequently not very basic about their terminology.
Tom and Harry couldn't believe that body chemistry is affected by simple velocity, since there are so many other nuances that do. The fact that the invention to make infinite vekocity was worked by them to a certain degree and the resulted speculation theory, using starfleet technology, could have propelled them to a different galaxy is rather conclusive.