Ultimate Clio and Gaz coilovers in the same sentence does not add up very well in my world. If you had written Öhlins or Yozza PSS10 it would have been more serious. By the way you can forget that dinky toy diffuser of the 197 addning anything worth mentioning to the downforce. Do a search on basic aerodynamics of a racing diffuser setup and you will understand why its crap.
Im sorry to say but if you want a ultimate track clio I think you are startning in the wrong end. Focus on the chassis to start with and lighten that car as much as you possibly can with that sorted you can start thinking about engine and anything else. You will benefit from weight reduction in all stages of driving, acceleration, braking, cornering the lot. God luck with your project.