Wow, 8/4 oak... up until now, I wasn't paying much attention to this product since I assumed it would be mostly for smoother surfaces like smooth surface or a carving base that's prepared. Nice. Would be cool, too, if it could be used for smaller vacuum pressings.
What it really likes holding is melamine and similar products. With that you can even turn the pump off. Rough sawn wood can be held reasonably well, but it depends on your definition of rough sawn. Some plywoods seem more "porous" than others so don't get clamped down as hard. I use it for planed oak no problem - the more i use it the more I like it.
I am hoping to get a hand held edgebander which should really make the VacSys come into its own.