The late 2013 Haswell 15" Retina Macbook Pro is the best Macbook Pro Apple had ever created. It's almost 2017 and it's CPU is as fast as the latest Macbook Pro. Read and Write speeds of 1gb/s and 16 gb of RAM is still very competitive too. The only reason why someone wants to upgrade is for the 460 GPU, the need for USB-C ports, the touch bar or simply the need of having the latest. Also the 2013 15" Haswell Macbook Pro has zero issues unlike the other models. I don't think there has ever been a Macbook Pro that has been able to stay so close in performance (excluding GPU performance. If you need GPU performance you should buy a PC) to the latest models after 3 years of age.