No worries, it's just that 300MB would be a pretty big piece of silicon to dedicate.
According dkanter's article here,
http://www.realworldtech.com/iedm-2010/3/, the 32nm eDRAM arrays are >11Mbit/mm^2 (density). Things may differ depending on performance target for the eDRAM & signalling or other design issues (e.g. Power 7 eDRAM arrays are quite spread out). Things may have changed since then, of course (process improvements & iterations). Power7+ die might be useful to compare there, but again, things will differ between how they'd design it as an L3 for P7+ vs a GPU or other (who knows).