[RichD]

The banked corners on a slot track do not have to be very steep to allow the cars to run flat out. If the cars have decent tires 15-20 degrees of banking is enough. If the banking is very steep the cars will tend to bog down and would probably run slower than they would in a corner that is not banked as much.

 

[RichD]

Here is an HO track with a very serious banked corner. I believe that it is 56 degrees.

This is the HO version of the famous 1/24th scale Purple Mile Sovereign tracks. It is located at LenJet Raceway and shares a building with Modelville Hobby that I think has the last 1/24th Sovereign.
I have only raced on the HO version a few times, but both higher downforce and gravity type cars are slower through the banking than they are in the straightaway.
There is a difference between a continuous banked corner and two banked corners that are connected by a banked straight section. The cars will tend to slide out more in that straight section.