Is there a meaningful performance index to compare various MBP generations?
Well for benchmarking you can download GeekBench or check out the benchmark scores for Macs.

My story: I still have my i5-2.5Ghz Macbook MD313 (2011) and I upgraded to 2x 240gb 560mbps SSD in RAID 1 which get speeds up to 800mbps. Then I upgraded my RAM to 16gb. It only has 512mb integrated HD3000 GPU and this 2011 machine outruns my 2013 i5-3.2Ghz 27" iMac with 8gb RAM and without SSD.

My advice:


Get a 15" non-retina (around 2012-2014) that has at least a 1gb dedicated GPU (2gb would be awesome), eg. the AMD/nVidia series and not integrated Intel ones.
For having 10+ apps open at a time, I highly suggest you upgrade
your memory to 16gb, anything above late 2011 can handle 16gb RAM.
Make sure it can support SATA3 and get a SATA3 SSD with speeds around 550mbps read AND write. (upgrade is easy)


The GPU will help with your Adobe suite (enable 'Use Graphics Processor' in Preferences). The RAM will help with 10+ apps open and leave most stuff in memory for faster opening etc without clearing memory that often. This will also help with Adobe suite as you can set how much memory it should use, the more the merrier, right? And the SSD will obviously help with opening/closing applications and read/write to and from files faster.

Upgrading older devices with latest products helps me out financially significantly!