Markus Barth, in his superlative Ephesians commentary, writes this about Eph. 4:11:
In summary, the task of the special ministers in Eph. 4:11 is to be servants in that ministry which is entrusted to the whole church. Their place is not above but below the great number of saints who are not adorned by resounding titles. Every one of the special ministers is a servus servorum Dei [servant of the servants of God]. He is a "pastor" of God's flock, who understands himself as a minister to ministers.
He adds:
Divers [various] books of the NT show that all "clerical" titles available from Israel's history and literature have been conferred upon Jesus Christ and comprehended in him. If after Christ's coming and under his rulership any legitimate clergymen are left in the world, then all saints and the whole church are these clergymen of God, installed for the benefit of those as yet unaware of the Messianic peace.
Pastor, I implore you to let Jesus have your title of "Senior Pastor" (1 Pet. 5:4). If you need an extra title other than "elder," why not use servus servorum Dei -- or simply "Servant Pastor"? That would send an interesting message to your congregation, don't you think?