Bandwidth is irrelevant if you assume both the X1 + Ps4's graphic cards are Saturated, we know the PS4 has double the Rops, more SU's GCN Cores so if both are saturated with data, Its all about the end product... The capability of the CPU and GPU, it boils down to what the Graphics Chips are doing.
Whats the point in having a 600BHP Car with Tyres that cant transfer the power to the ground, adding Esram bandwidth figures and expecting the X1's Graphic chip to utilise more than it needs is pointless. Bandwidth is not Storage space, thats why the GDDR5 is clearly going to be holding far superior quality textures and general data at 1 time.
What X1 needs is to utilize tiled resources on that 32mb of EsRam, use 16mb for a frame buffer and the other 16mb for a tiled resource target file that can STREAM textures from a file upwards of 10GB, but it requires developer optimization and is possibly the X1's version of the PS3 Cell, a pain in the ass, its a botch job versus the PS4 ease of use + better hardware. But its definately a help if the developer puts the effort in.
The problem with that is X1 GFX Chip only supports DX11.1 and can be upgraded by software to DX11.2 TEIR 1, which means it cannot do the same things as the PS4 Card supporting DX11.2 TEIR 2 Tiled resources potentially. (Software DX11.2 vs hardware DX11.2)