The SportContact6 is just better all round on the M3. Less road noise to the point of mostly hearing just wind noise on the motorway, much better wet performance (you can feel it in the steering wheel and how composed the car is now vs the PSS) and the rim protection is a bit wider too so a bit of extra kerb damage protection.
It helps that the CSC6 are cheaper too.
As for size, go with whatever you prefer. I chose CSL size on stock 19" wheels. The tyres fit just fine and are an acceptable upsize. The standard rear alloy is teh same width as CSL anyway, the front on the CS is half an inch wider but the standard alloy fits the size perfectly anyway.
Let's face it, PSS are old news now and there's a cheaper and better UHP tyre on the market
It helps that the CSC6 are cheaper too.
As for size, go with whatever you prefer. I chose CSL size on stock 19" wheels. The tyres fit just fine and are an acceptable upsize. The standard rear alloy is teh same width as CSL anyway, the front on the CS is half an inch wider but the standard alloy fits the size perfectly anyway.
Let's face it, PSS are old news now and there's a cheaper and better UHP tyre on the market