Going with the biggest recommended is the best plan, IMO, but just be careful with them. They will be extremely responsive and too much trim input can make the boat respond dangerously/unpredictably.
That said, my 25 footer came with little 12x9s and they are quite effective and useful despite being under-sized; so if you can't fit the biggest, under-sized tabs will probably still make you happy. The factory tabs on my 44 footer are under-sized as well, come to think of it. Guessing it's a liability thing...
