Hi Wouter,
"So who wants to take on this job and work-out a summary of what is often used/available on the (second hand) market in the way of Race and Formula sails. Also check what sail area's and luff lengths (+mast lengths) are used in 8-15 knots conditions. Boom lengths are important as well. "

VERY brief summary - Formula Racing requires that you register 2 sail sizes for an event - you may only use these two sails at the event. Most guys register a 11/12,5sqm sail for light winds and a 8,5/9sqm for heavy winds. Light winds are 8-15knots, where up to 12,5sqm sails are used, from 15knots to 30knots (cut-off) they are using 8,5sqm or 9sqm sails.
I think I`ve answered on the luff length and boom length questions in a previous post on the size of these sails, but a quick look at www.neilpryde.com - sails - racing - RS6 will give a complete table of sail sizes and their specs, and will take you a lot less time to look it up than for me to figure out how to.. wait a minute.. see attachment !
Hope this helps.
Steve