If this doesnt work for you one sure fire way to calm down a loose board is add some weight to the rear by adding a 3/4 patch to it. I did this to an extremely loose board and it stablized the rear making it an excellent ride for bigger days.
Sounds weird. You say it doesn't work in eastcoast 5+ but you expect it to work in 5+ at other spots around the world? Going from a board that works in medium size eastcoast waves to 6+ waves you may reconsider boards. I don't know anyone who has a medium. Board and expect it to surf in step up conditions. I have a 5 fin fish with a wide tail that can handle small to medium surf, then I have a shortboard ffor medium surf, and then I have a step up for head to DOH. None of them have a tail with the same measurements. Fins won't help when your tail ain't right. Your rails also have a lot to do with hold. If your on a flat face short period vs. A walled out sucking up freight train you better have choices. Tell your shaper and he'll set you up with what you need. Good luck.
Been on the knubuster. Mixed feelings, but I have no computer here so will post ob Monday.
So I was riding the Knubbuster on 2-3 foot swell and 4-6 foot swell.
Here is my quick opinion:
Overall, the board feels like you are a slot car on a race track. The board looses a bit speed but gains stability. In smaller surf, I didn't like the knubbuster because you lost a lot of speed that can help you get over some ****ty sections of the wave.
In bigger surf, the board is more stable and tighter. The board holds well, but again, you lose speed and bottom turns don't feel as "loose" as they would on a normal quad. The board pretty much feels like you are a slot car on a track. Not a bad thing, depending on conditions.
People are either going to love it or hate it. I was surfing on a 6'2 in San Fran area and it really came down to conditions. Would I use this everyday? no. Would I use this once a month? Probably not. The knubuster has its place though, but in anything over 6 feet, I will stick ot a regular thruster.
I like the new MF-1 fins as well. They feel the best in a thruster.