Well, I looked through the approx 400 pdf file.
Hopefully they stick with the metals and materials proposed for the skin of 910' tower.
If memory servers, there is a footnote about the fact that exterior materials "may change" due to price conditions. Hopefully, they do not go cheap and/or the planning deptartment does not let this happen.
But heavens... forget the 600' tower. Personally, I really don't think this is a foster tower. Basically, they cut and paste the materials and design of One Market Market Plaza. Sorry, One Market is an eyesore and the planning dept. should have known better to let them build an even taller version.
And yes! I know it is approved and basically a done deal as long as the economy remains strong.

source: me