An excellent presentation on this topic was given by virtualization expert Dr. Bernhard (Benny) Tritsch at Teched 2010.
Benny’s slide deck and a video of his presentation are posted on the Tech Ed site.
PCoIP over WAN 200ms no problem.
Used hardware: these tests were conducted on an Atom-based thin client connected via VGA to the Samsung monitor NOT in HW zero client mode. (Samsung monitor)