Interesting page that reviews FSW boards back to back (a year old):
http://boards.mpora.com/equipment-tests/tested-equipmentWithout knowing your age, fitness level, progression (and I could only know that if I met you in person and saw you sail) and seeing your location and how it works, I'm a bit necessitate to recommend.
I normally blast around on an 85L FSW board with either a 4.0 or 4.7 freeride sail from F4-7 winds (and F7 only just) which is what we normally get here in summer (subtract about 5 knots to this due to our warmer/less dense air compared it to your colder/denser winds in Ireland). The other day I was blasting around on my 69L wave board and 4.0 sail combo in 25-30kt seabreeze (which I'm stoked about - 2nd go on this brand new $600 'clearance sale' wave board I brought a few months back for cyclonic Ardrossan sessions in January, but is good for afterwork sessions in Adelaide). For me, being a average windsurfer and sailing 5 years, it took a bit of time to work up to this small gear.
There's guys at my local who became advanced within a season (from beginner to carve gybe/duck gybe/forward loop/waving riding in places that would be beyond my skill level and fitness).. So, it wildly depends on your ability. It's a hard one. I doubt I would have the skill/fitness to sail where you do. When I think of windsurfing in Ireland, I think of the 2006 Redbull Stormchase Challenge documentary.
Sorry, if this tells you absolutely nothing