"When you think about it for such a light car do you really need large venting discs, especially when the existing discs are stuck in the air stream anyhow."
No.
Alcons = MUCH Less weight (+ Magnesium wheels? the way to go), less cost, less hassle fitting. Jimmy the Fish has sussed it.
Do you sprint or hillclimb? Do you drive in the real world? Then you DON'T need vented disks... or do you go to work down an alpine pass?
No contest.
Andy