[jbrechtel]

Unfortunately, the real problem here is a broken API. A statically typed language whose standard library includes APIs that require downcasting is pretty embarrassing.

In general though, if the situation is truly exceptional (wrong type being passed) then counting the ticks used throwing the exception should be compared against the ongoing cost of the increased complexity to the codebase to handle the exception in another fashion (e.g. an if/else block).

Also, if you're just comparing the ticks of as+is VS invalid cast wouldn't you want to multiply each by the # of times they'll be executed? The as/is would be executed EVERY time the function in question was called. The invalid cast would, in this case, likely be executed once or twice ever and then the bug that is causing an InvalidCastException would be fixed.