I was trying to find out about the spoiler as when I bought my 5 door there were no pictures available of the hatchback. Since I drove the large spoilered saloon for 2 weeks I ordered the "small" spoiler on my ZS. Even when the it was delivered I got a "oh yes, it's the small spoiler", and I couldn't contradict the dealer without evidence!
The strange thing is, my car IS fitted with the large spoiler, the reason given for delay in delivery...shortage of the smaller spoilers. I wouldn't swap though, the 4 door large spoiler is a bit intrusive, on the 5 door isn't, and it looks pretty cool too.
PS had to drive on the motorway once with standing water and rain with little other traffic, I reckon they got the aero working quite well if my vapour trail was anything to go by, and it feels pretty stable at speed.