Ship Simulator 2008 places Titanic's engines' top speeds at 75 RPM, while, according to Encyclopedia Titanica's article on Titanic's propulsion system, it could reach 80 RPM maximum. Infact, Bruce Ismay said at testimony that they were planning on reaching this RPM towards the end of the journey to suprise New York with an early arrival. The ship did not survive long enough to see herself traveling at 80 RPM, though.
Her top speed was 23.75 knots, but the game cuts it off at just over her service speed, 21 knots.