RE: Pros and cons of smaller sails on Formula
Freerace sails are more grunty, especially if you're looking for earliest planing in lowest possible wind because that's their primary design focus. A pure formula racing 11 m2 sail will have much more top end range than a 10 m2 freerace sail, again because that's their design focus. If you're not racing and don't want to have the maximum performance at all costs, then a freerace sail is a perfectly viable alternative on a Formula board IMHO.
As for durability between freerace and racing sails, I can't comment personally but my '98 ART TNT6 8.2 sail lasted 5 years and my '00 NP RX2 10.6 lasted 7 years before the monofilm started to become brittle and develops cracks everywhere. UV exposition while sailing is the sole and unavoidable culprit. The two battens above and below the boom on each sail broke late in their lifespan but were fixed quite easily. The top shear tip batten of the NP RX2 broke and was lost to sea (fortunately, I'd made lenght x diameter measurments of all battens when the sail were new, so it was easy to get a new home made shear tip).
Both a '98 North Viper Race 510 cm carbon mast and '98 North racing 220-260 cm carbon boom lasted 5 years before breaking. The mast melted and bent at a pressure point facing the top camber of the ART sail (rig left in the sun in a rig bag but I forgot to release the full downhaul) whereas the boom broke at the junction between the front boom tubing and front clamping head (obvious design flaw).
So in sum, a freerace sail is fine as well, you can't go wrong, especially on the co$t issue.