Well, compiling and running the above I get:
cast: 4.96
as : 2.46
Without the try/get:
cast: 0.83
as : 1.61
Removing the calculations and the check != null for as (so you have only one cast), I get:
cast: 0.83
as : 0.83
So they are the same if you don't have a try/catch. Putting the calculations inside a catch might be unfair, in the sense it will also "try" to catch exceptions for the calculations as well, without a reason.
Finally, without a try/get a cast is 2x faster. So generally I would say if you know what you are doing, like casting a TextBox in an event handler for a TextBox then the cast is faster, because you won't have to try/catch (if the "risk" is acceptable).
Within a try/get they have the same speed
