RE: looking for advice buying a new board
I'm a freerider myself (progressing, still have trouble waterstarting, but hey) anyway... I surf with a starbord Go 139 from the 2006 range. it's a really fun freerider, with the right sailsize (for your partner, i weigh as much as he does, 7.5 m?? would be magnificent in about 4.5 BFt -5 BFT, i guarantee). you can hit speeds that will makes your toes curl of adrenaline. However i'm a bit dissapointed with it's low wind prestations. The go offers you multiple footstrappositions so you can vary it depending the rider.
Another good board in the Starboard range is the Carve series. Anything above the carve 122 is comparable to the Go and allows inward and outward footstrappositions. Both these boards have an enormous sailrange and can be used in mild choppy waters (i tried the Go in a wavy condition, BAAAAAAAAD idea!).
Mistral offers you the Explosion, which is a large freeride board, it's quite wide but small all the same which will make jibing a childs game. Also the larger Sreamer (so thats the 115) would give you that extra trill, but considering the conditions you both surf in (which are comparable to mine) i suggest a bit o a bigger board so u can still haul the sail out of the water if there isn't too much wind (so 120-140 L)
F2 offers the Stoke which is a strait edge freerider. you can check it's review on the F2 website etc. F2 is one of the oldest brands and over the years did deserve a lot of credit. The Stoke has a big range of liters so there's plenty of choice there.
But all in all, i can agree with what Lampi has said. I just gave you a couple of names (looking for a new board myself, though i know i'm sticking with Starboard, you just fall in love with the qualities of those boards - speedmachines of the greatest kind)
i just want to give you one more tip and that is to get a wide range of sails with your board. Mine reaches from 5.5 to 7.6 and i manage to sail on flatwater between 4 BFT to 6.5 BFT without any problems and with genious speeds (thoguh in 6.5 BFt i look really silly with my 139 L board between all the 98 L guys with the same sailsize as mine, but still, it's the spirit of the sport that counts, not the material)
Hope you find what you're looking for.
greetz - Haiko, aka crazychemical