Bob,
The only available urethane tires I know of as Alwyn has stated are Super Tire Yellow Dogs and Paul Gage. Super Tires has a monthly 25 dollar special. You can get 6 pair of Silicone or Urethane for that price. If you want to mix things up this month they have a make your own special. There is a list on the website for tires to fit the new Scaley Monte Carlo.
I have run both types. I had 2 Cudas with them and they both turned about the same lap times on my Scaley Sport track. The gearing was slightly different and one car was 14 grams heavier. One with a stock chassis one with an Olifer. The stock chassis heavier car with the higher gear ratio and Yellow Dogs was .78 secs faster.
Now mind you in the first round of the 2018 TransAm proxy the lighter car on Paul Gage tires finished in 8th place. The heavier car blow the gear in lane 2 but had equal times in lane 3 and was 1 lap down in lane 1. So my conclusion is that both tires are about equal in performance. Guess you would have to set up both cars the same to know for sure. But then the motors might not rev the same. RichD has stated you can set up 2 cars the same and they still may perform differently.
Do you plan to enter this in the TransAm proxy? Would look forward to going against you.
Use this information at your own risk.
Your car looks great with the inserts.