Thats not a really a fair comparison in relation to X1/PS4, simply because the 7770 can only issue 1 triangle per clock, whereas the X1 GPU can 2 (same as PS4, no differences there).
Moreover the X1 GPU has an additional 102/4 GB/s to the eSRAM which schould help the ROPs (12,8 GP x 8 Bytes per Pixel = 102,4GB/s
; btw the PS4 cant really use the 32 ROPs: 25,6 GP x 8 bytes per pixel would be 204,8 GB/s)
I think when we take sebbi explanation, the differences in mutli platform games will be 1920x 1080 for PS4 games and 1600x 900 for X1.