Silicone vs Urethane Tires
My instant take (subject to change). Based on Carrera track and car after turning several laps. For starters I have semi-trued the urethane and simply tried to "level" the silicone tires once mounted. So I guess it's not truly a fair test. Although that is how I would use them so for me I guess it is... However the issue itself might largely be moot as looking for silicone tires for my two Ferrari FXXs they don't appear to exist.
Now I can tell the silicone's aren't trued by the amount of the tire that doesn't get dirty. And dirty they do get... I guess from my hundreds of urethane laps plus my truing sessions. Even so they appear to have more grip. As an example I can plow through the esses as the car stays on a straighter line under speed. When accelerating it feels like the tires are stuck to the track either slowing or speeding you up... I'm not sure yet.
For me it's not about which is faster, rather which is more entertaining to drive. At this point I'd say the urethane as I know their limits better. I'm guessing once I get used to the silicone tires they might be faster and offer a little more of a challenge as I can push the car harder.