Infusion seems to be the way to go, but you only get one finished face with peel ply texture on the other. What's the best way to get 2 finished faces? I tried a small 150mm square by just clamping 2 peices of aluminum tooling plate together and it worked perfect with really good fiber to resin ratio, but I need some larger 500x500 plates (2mm thick). I could use 2 plates of glass backed up by something else like mdf maybe, but I imagine just clamping around the outsides is not going to squeeze the middle well enough unless I get tricky with the clamping. Maybe some thick peices that span across with clamps on outside to hopefully put enough pressure in the middle. 
Any other good way to do this other than clamping? If clamping is the best option, what's the best choice of clamping plate material and method for doing it? 

Out of the three cores I mentioned, soric lrc (lrc is the lightweight soric version) is the heaviest one, but acts as a flow media. Not as good as regular flow media, but good enough. The density of the core after infusion is far below 1g/cm^3, while solid carbon is around 1,6g/cm^3. In my applications a similar laminate with 1,5 soric lrc flows in water.
The closed cell foam cores are far lighter in comparison, but do not make a huge difference when it comes to thin cores, as the core surface takes up some resin, and thin cores have more surface per volume than thick cores. they will be lighter, still.