Yeah it's the dark wheel arches that make the wheels appear bigger. This is really clear if you compare 18s on an SE with the Chicago M Sport's 18s IMO.
It's a tough one alright marmite
. Thankfully the decision never had to be made by me as there was no M Sport available when I ordered.
It sounds like you fancy the M Sport so go for titanium silver as it's closest to white. 19" alloys, black Nevada interior and a sunroof
Bear in mind those titanium silver pics are a bit artificial given all of the bright lighting at motor shows. You really need to see one in the flesh