Here is what I found when I was researching the media.
Sera Siproax surface area 270 m2/L (this also may be a gross underestimation)
Due to the small pore size, the pores do not clog. Pretty much legendary for its trouble free performance
Seachem Matrix surface area >~700 m2/L
Although when tested against other substrates in an independent test it was over 2100 m2/L
http://www.greenaqua.hu/docs/Specific-Surface.pdf
Marine Pure surface area: 1300 - 1700 m2/L
I find that hard to believe with the large pore sizes they have.