Target display mode - did it have performance issues?

[TheCopywriter]

Apple has disabled target display mode for the new imacs, so I am thinking of waiting to get one.

My question is, do the old imacs (in target display mode) have performance issues? If I wanted to use it for gaming would there be any lag between my PC and the imac as a monitor?

 

[MadDane]

From just performing a quick Google search it seems like there is no noticeable input lag. But to be honest I have never tried gaming on my late 2009 iMac using Target Display mode.