If you can get away with it I'd go 20% I had it on my R32 and loved it, if and when I re-tint my car thats what I'm going to go with. I think the M has 35 on it now, it seems a little darker than that though. It came on the car which came from s-fl so who knows..?
My G35 with 35% (no color correction) After getting it, I wished I had the 20%...
