It honestly depends on what you are rendering. If your application is just pong, it is feasible to implement a rendering pipeline that is virtually instantaneous. GPUs have overhead for even the most trivial application. With flip-flops or other analog circuitry, you are talking about frame latency in terms that are similar to the propagation speed of an electron through arbitrary copper wires or semiconductors. If you insist on digital output, some buffering will be required, but in the analog output case you are probably looking at a handful of microseconds of latency between input and output.