stay sail size?

[voyager35]

Having just fitted a removable baby stay for my stormsail I have now started thinking that a staysail might solve some of the problems I get going upwind when heavily reefed. The genoa is quite big (main 190 sq ft genoa 340 sq ft) and when more than 30%reefed starts to lose shape and so upwind performance is lost.
The question is what size staysail should I aim for and how much overlap of the main is needed to maintain good performance
The new baby stay will give a luff of 20 ft and a j length of10ft

 

[voyager35]

Having just fitted a removable baby stay for my stormsail I have now started thinking that a staysail might solve some of the problems I get going upwind when heavily reefed. The genoa is quite big (main 190 sq ft genoa 340 sq ft) and when more than 30%reefed starts to lose shape and so upwind performance is lost.
The question is what size staysail should I aim for and how much overlap of the main is needed to maintain good performance
The new baby stay will give a luff of 20 ft and a j length of10ft

Rather surprised I didn't get an answer to this question, do you need more information?