A 7870 (rebranded as 270X in this chart) is 30% faster than the GTX 580 in the modern era at 1080:
http://www.computerbase.de/2015-05/.../#diagramm-rating-1920-1080-normale-qualitaet
At the launch of the 550 Ti, the GTX 580 was 2.25 times faster than a 550 Ti at 1920x1200!
http://www.computerbase.de/2011-03/test-3x-nvidia-geforce-gtx-550-ti-sli/24/
In what universe are these cards even remotely equalized? Minimum requirements can be complete rubbish sometimes and this is a shining example.
yes, the 550 ti is normally slower than the 7770 (which is half a 7870)
the min CPUs is also BS, i5 2300 is much faster than the 945
it could beat the 975 (600MHz more) by a good margin
http://www.xbitlabs.com/articles/cpu/display/core-i5-2500-2400-2300_7.html#sect0