Ok that makes sense, I was using the default damping on Z (5), now that I know it was for a boat I will try out some different values. I fixed the majority of the angular rotation issues, and the buoy no longer stops suddenly at a certain level like it did in the video.
The performance is getting a bit better, still fairly heavy on the CPU (22ms for the scene in the video, 45fps on a GTX 980 / i5 4670k), just the simulation runs at 120fps without the added CPU calculations, so it is just a tad bit concerning… I intend to try reducing the large waves down to a single cluster of 8 and use those to calculate buoyancy, and use the other cluster for detail waves. The other thing I have been testing is only applying force when the test point is under water, and letting the built in gravity do the rest. I might leave for now and release an “early adopters” version with the system as is then update again once I get the performance to a reasonable level.
Actually I think I just realized what is causing the performance drop… Will post an update later on if I’m right!
The problem I have currently is setting the buoyancy value to 1 causes the object to sink almost to the bottom, come back up and jump out of the water, then sink back down again. Once it finally settles, it still sinks down too far. Is it possibly the mass of the object is too high? Or should the test point volume be increased to compensate? I’m still trying to find the best solution, other objects work just fine at 1, but to keep the buoy on the surface I have to bump it up to a minimum of 4 currently… 
So it’s coming along, getting closer. Thanks again for all your help!