Added a couple more cores and 12 more gigs of ram to my T520 : r/thinkpad
16GB KIT (2 x 8GB) for IBM Lenovo ThinkPad T Series T420 T420i T420s T520 T520i. SO-DIMM DDR3 Non-ECC PC3-10600 1333MHz RAM Memory. Genuine A-Tech Brand. at Amazon.com
Tuning the Lenovo T520 - Upgrading Memory and Installing an mSATA SSD • Helge Klein