Dave Hill has raised the question in Round the Island about the relative merits of using both genoa and staysail or just the one when sailing upwind.
To my way of thinking if an effective slot can be acheived between the two sails in addition to a slot between foresail and main it should give more drive.
Acheiving the required setting without backwinding the main or choking the outlet from the foresail slot is difficult as the CC19 has no adjustment on its foresail fairleads or Barber haulers but if serious racing is the order of the day then it should be attempted.
I now fly a yankee with the staysail and try to get both sets of telltails flying even when just pootling round Rutland Water where the task of getting from A to B is a matter of a few miles. In stronger winds the yankee or staysail is dropped and a reef put into the main.
Dave Stafford on Ida ( a beautiful self build CC19) has had a blade yankee made by Jeckells which barely overlaps the forestay and which he flys all the time with his staysail and swears by its effectiveness.