Just to give you more than the two and a half words I've written as a comment, let's get down to the processor level and try to find out what the difference is there regarding this question.
First, a processor always loads a full register size of data whenever anything needs to be processed. So the least data loaded, wheter you use it for a binary or integer comparison, would be 32 or 64 bits. Let's assume 32 for the moment.
Then, the difference between the two is this:
Forgive me if my assembler is not right on the spot, it has been about 13 years. But the answer still stands. The difference between these two should at the current processor generation be practically zero.
Then, there's the engine of the RDBMS. It might translate your CASE statement into something like the assembler above, but chances are that it transforms it based on it's own rules.
Then, there's the query optimizer. Whatever it does can be determined, usually by something like EXPLAIN (in MySQL), there's a similar function in MS-SQL-Server that explains the execution plan.
Then, for testing the speed, you need an environment that can ignore the interference from different processes, caching mechanisms and the likes.
So that all makes testing such things difficult, and the results speculative at best. Usually the time spent figuring out such little differences can be used to much greater use by optimizing indexes or data structures, server parameters or SELECT statements.