I guess the question I should be asking is what is the gospel? like what are the essentials to the gospel and what are the boundaries where we say so far and no further. i think though the answer is as you say in the historic reformed creeds and confessions.
thanks again I shall read the articles.

1Jn 5:20 And we know that the Son of God is come, and hath given us an understanding, that we may know him that is true, and we are in him that is true, even in his Son Jesus Christ. This is the true God, and eternal life.