As a comparison:
I have an older Starboard Formula 186. I think this was the first of the 100cm wide ones and was quickly superseded in the same year by the 186X so it was still in fast development. It is not even wood construction but is plenty light enough. The first time I sailed one the same I was sailing my light wind slalom board of about 130 litres with a powerful 6.5m sail but the wind dropped to less than 12 knots and I could not keep planing. I pulled into the beach and a friend offered me a go on his Formula with 8.5m sail. I accepted but decided to try my 6.5 instead (such a 'huge' 8.5m sail freaked me out back then

). I was astounded that as soon as I stepped on the board I was planing easily after 1 pump. Not only that, I was able to sail upwind and downwind at will. Remember, this was with the exact same sail that wouldn't even get me planing on my large slalom board!
Conclusion (since backed up by numerous other similar experiences:
When conditions get marginal, switching to a much bigger formula type board is
much more of and advantage than switching to a bigger sail.
A couple of years ago a picked up the same model board second hand for $500 in great condition. I have had endless hours of fun ever since on days less than 10-11 knots when no slalom boards could sail at all. First with a 8.4m KA Koyote camless sail and later with a 9m KA Koncept. With these sails I can easily cruise up and downwind in 8-9 knots+ (perhaps slightly less)
But,
When my friend Mat comes down with his modern Formula board and state of the art 10.8m rig with carbon mast, boom and adjustable everything (picked up for a bargain price BTW, after an international race in Melb. from a broke top French racer

) he does out run me upwind and downwind. Not by a huge amount though, and if he fluffs a tack occasionally it can be enough for me to stay with him for a while. Clearly for racing performance/competitiveness you need the mega rig, but for light wind fun where you don't have to get the last few degrees up and down wind there is very little in it and you would probably hardly notice the difference.
I can run the 8.4 on a 490 80% mast and alu boom. Not that expensive. The 9m Koncept does require a 520 mast but I still use a $250 alu boom and it is fine. Actually, it doesn't make much difference for cruising to even use my 7.5m Koncept which rigs on a standard 460 mast!
Once you get the the 8-9 knot mark or thereabouts, you need another couple of thousand $ worth of gear to lower the wind minimum by each 1 knot step. Not much different from how it's always been but back in the early '90's the big $ threshold was more like 15 knots. Thats
big progress I recon!