Performance info on "Emulated" LVDS Outputs?

Hi - Altera mitigates the lack of directional programmability on their LVDS I/O by supported "Emulated" LVDS I/O that allows you to turn a native LVDS input into an "Emulated" Output. But even after several web and doc searches, I can't find any info on the relative performance of these "Emulated" Outputs.

Does anyone have any information on this? There was an old forum thread where it was asked, but not answered..

Thanks!

/j