Is more then geforce 460/560 required even for 1x Internal Resolution.

[AnyOldName3]

Then it's likely not the horsepower of the GPU, but something else. It could be:

Access to RAM
Access to VRAM
Access to HDD
High load on weird part of pipeline than no PC game uses much, so isn't very powerful
Long list of complex calculations which depend on each others results, so less than 1 IPC is achieved as results must be loaded from and written to cache/RAM