I think I have the XL one. XXL might become a proper unweildly monster if youre not careful.
With the size of your cars, going from memory here, you should be dandy with just the XL one. I think I did a Disco 3 with mine and it was only as I got to where i'd started that i got any kind of streaking.
Just remember never to wash them with fabric conditioner as it makes them hydrophobic. My beloved (sarcasm) ex-wife did that to all my towels. I think, napkin maths, she fucked up £400 worth of stuff that day.