Oh hai, in this thread I'll be taking a look at C5's in games(as I find them) so I'll start with one I can remember.
In 1985 the budget label Atlantis published Revenge of the C5 written by Barry Jones. In the game you take control of Sir Clive's personal C5 and are challenged with winning British Cross Country Finals while avoiding traps set by the sour British press.
It's typical budget fair but it's got a certain charm as you hurtle forward with no brakes and have to dodge slightly strange stuff like palm trees and ghosts.(Every C5 drivers nightmare)
The game over screen gives you a nifty report on your progress with a C5 whizzing along.
The game and further info can be found here:
http://www.worldofspectrum.org/infoseekid.cgi?id=0004117