There are some differences in the suspension, steering, brakes and the ECU is different, plus they are 89kg lighter.
Having driven both a mk2 172 and a Cup for a good few miles (mates Dad owns local Renault dealer) I was surprised how different they were...
The Cup is a sharper drive than the normal 172 and there is more of a surge at 5000rpm, when it comes on cam, like the older mk1 did, but you still get more low down grunt that the mk2 has, but the mk1 lacks.
Cup loses air con, ABS, leather trimmed seats and xenon lights and sound deadening but is 2k cheaper.
Gains wider track, lower suspension, different ECU with improved response, larger brakes, different alloys, only available in blue, Cup badging. 89kgs lighter than the 172.
Is quicker than the 172 but not by much, steering response is better than the 172. Drive both and if you could go without the goodies you will prefer a cup.
By the way the Cup is full UK spec, in the EU its badged as the Clio Ragnolli.
172s can be bought from trade-sales.co.uk for 11699... All come with Renault 3yr warranty. Cups can be bought from dealers from 12k ish.. rrp is 12999..
I got a new Cup a couple of weeks a go, generally very pleased, goes like a scalded cat, very grippy. Real world,its not appreciably slower than my integrale was; it is very fast, lots of fun, and excellent fuel economy. Also quite stealthy, you can surprise a lot of other cars with it's pace. Should be very good on track as thatr is Renault's stated raison d'etre for the Cup.
Cup is quicker than a standard 172 untill you come to brake hard in the wet at a roundabout. Then the 172 slows and negotiates the roundabout while the cup dissapears straight on through the trees and grass into a heap.
Buy yourself a 172, go to Janspeed and get a de-cat exhaust, then you can play with the cup boys while you sit in your climate controlled atmosphere listening to ya 6 stack CD player from your leather and alcantara seat ......haha