Can a flip flop possibly work at over 800MHz?
Here is a D flip-flop spec'ed to operate at 40 Gbps. Setup and hold times are advertised as 4 ps. It consumes only about 750 mW.

These are manufactured with a SiGe process, although I don't know which one.

There are several foundries offering SiGe process, including GlobalFoundries, TSMC, and TowerJazz.