Yep, Gail's article conclusion tells that it doesn't matter what you type between SELECT and FROM in EXISTS query, as long it represents valid T-SQL sytax, SQL server always does exactly the same thing.

I will not be surprised if SQL query engine (parser or compiler) strips all things typed there and replaces it with some litteral constant (most likely "SELECT *") before performing the query.

So far, all suggestions that one sytax performs better than another are just unproved speculations...