The W520 that I use consists of Intel i7 2720QM, Nvidia Quadro 1000M, 1920x1080 matte screen (non-glossy), 128GB SSD and 9-cell battery.
This laptop is totally high-end, both the specs and build quality. Although it's a typical plastic Thinkpad case, laptop feels very solid, every part fits perfectly and it also doesn't overheat.
The most suprising thing about this laptop is the battery life. My w510 worked 2 hours at most, and for W520 5 hours of work (browser + IDE + a virtual machine with SQL Server and IIS) is something really easy.
Second most impressive feature is it's beautiful Full HD screen. The resolution doesn't feel any bit too big, it's just perfect for writing. browsing and simultaneous work on many windows. It's also non-glossy and although it hasn't the most stunning viewing angles it performs very good in outdoor conditions.
The processor feels very snappy, with 8-threads and hardware virtualization it's really a powerful workstation. For gaming the graphic card could be better, but it's a workstation, so it isn't it's main purpose. I don't process any data with GPU so I shoudn't be complaining about it.
The least satisfying is performance of SSD drive. Of course Windows boots down even 4x faster than on W510, but in my software development work I didn't see almost any improvments in performance. I don't know who manufactured this SSD, but it for sure isn't the top of the line drive.
W520 is a powerful workstation, ideal for working with dock and multiple screen but also "on the run" (however it's weight could be a problem for longer trips). Of course it's price is even more shocking then it's performance and this will be a good choice only for the most demanding users, those who use it in their work.