have you had it MOTed since you fitted the cinq wheels? might be an idea to keep the originals just in case. also they may be usful if you ever sell it.
i have cinq alloys on mine and while they are mostly in the arch a little sticks out, technically it should fail its MOT.spose it depends on how strict the tester is, after all one sees loads of Corcas and 4x4s with their wheels stciking out a lot more than our little 126s.
I'm keeping my 5 original wheels (I have a seicento sporting space saver as my spare; fits perfectly) just in case i ever need to take the alloys off, besides i doubt you could get much for the standard wheels.