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My MacBook Pro is also the same age as your, but it was a mid range model with a dedicated graphic card, it still work pretty well running Photoshop and Lightroom but can be further improved by installing an SSD to get a few more year out of it, annoyingly the RAM maxed at 8GB.
I'd go for the high end model if you can afford it, you can able to get 7 years out of it easily.
To be honest, it sound like a desktop computer would be more beneficial and the last a lots longer (32GB max ram), unless you really do need a laptop.