Re: Overlapping versus Blade headsails which is quicker ?
Simply look at JeffH's avatar ....
Youll notice immediately that the leech of the jib is (for the most part) operating in close proximity and 'just before' to the 'point of maximum draft' (POMB) in the main. What this positioning of jib's leech to POMB of the main is doing is yielding maximum 'bootstrapping' of two sails or which affects the best 'dumping velocity' from the jib to the main ... for maximum interaction flow between the two sails. Once the jib leech overlaps beyond or aft of the POMB of the main, aero-efficiency of the combo will start to rapidly decline .... although one can 'muscle' more speed (but not necessarily more 'lift' in direct proportion to the increase in SA) by increasing SA with a larger overlap.
I perceive this configuration is why the 'modern' frac rigs are generally carrying a lower LP jib and rarely a large LP jib ... for the combo of best boat speed AND pointing ability irrespective of 'sail area' considerations alone, ... also ignoring the geometry problems associated with sheeting angles on large headsails.
Whether this config. was determined aerodynamically or simply iterated by trial and error, it 'seems' to be in accordance with that which theoretically generates maximum aerodynamic conditions and output.