I have had a 172, and currently have an '07 Fiesta Zetec and 225 Megane in the garage. Is your Fiesta the WQ, or the later WS model as I believe 2009 is the year that the new model came out? I actually have both of these as well, as it turns out. The WS Fiesta is a LOT softer than the WQ as it never came with sports suspension (the earlier WS did, and the latest WT does) but rather, it has the same setup as the lesser models (CL, LX, Ghia).
I moved from the Clio 172 straight to the WQ Fiesta and while I found the Clio a little more balanced and manoeuvrable, the Fiesta has far greater corner speeds and road holding. A well sorted Clio 182 will return the Clio to front-runner status. That, and the Clio has a far better engine and chassis.
I am selling my WQ Fiesta, but as I do have this car, the WS and the Megane 225 at the moment I can say that if I have the choice of any drive on a nice weekend I will pick the Megane. If I'm going to be stuck in traffic then I'll generally pick either the WQ Fiesta or the Megane. The RSM is more enjoyable, but it is more hungry for liquid dinosaur.
Reviewing your criteria, the Megane will feel "bigger" in terms of it's handling charateristics. But only marginally. Given you'd also like to track the car, and I suspect you'd like to win in a class, then the Clio is definitely the one for you as trixie has stated. If you're after something more comfortable, but equally as fast as the Clio when you need it, then get the Megane. You'll just not be competitive in your class.