I would recommend Lenovo Thinkpad W520. As you probably know, Lenovo purchased the IBM personal computer business and the ThinkPad brand in 2005. T43/p & T60 were one of the last IBM-designed units.

Note: I own this laptop and it is just my personal view. I faced with a similar choice - solid workstation that will last for years. I bought it as an off-lease laptop for $400. In my humble opinion, it would be very difficult to get something better for this money. Answer is based on a 4284XXX model.

[Specification (for versions: 4284W85, 4284E57, 4284B26, 4284A35)][1]:

 - Processor: Intel 7-2820QM with quad-core
 - Graphics: Nvidia Quadro 2000M, HD 3000
 - Memory: 8 GB DDR3-1333/PC3-10600 (maximum memory: 32 GB)
 - Maximum Battery Run Time: up to 10.80 hour (9-cell) or up to 21.6 hours (9-cell plus Slice battery)
 - HDD: 320 GB (Serial ATA/300, 7200 RPM)
 - Screen size: 15.6" (Active Matrix TFT Color LCD, 1920x1080, anti-glare display)

What distinguishes this model from the typical consumer laptop:

 - palm rest does not bend in too easily under pressure 
 - solid hinges 
 - you can open the display up 180 degrees

Classical Thinkpad keyboard may be a plus for you. Check the difference [here][2].

Check unboxing video [here][3].

Check product gallery [here][4].

[![enter image description here][5]][5]


  [1]: http://www.pcworld.com/product/compare/1298934/lenovo-thinkpad-w520-4284w85-notebook.html
  [2]: http://forum.thinkpads.com/viewtopic.php?p=680454#p680454
  [3]: https://www.youtube.com/watch?v=ythPaRrzRsA
  [4]: https://picasaweb.google.com/lenovocomms/ThinkPadW520
  [5]: https://i.sstatic.net/CisvT.jpg