I was thinking about the same two and decided that the only difference was that 20.1" Iiyama PLE511S-B has speakers. Apart from that they could be the same panels in different boxes.
Look here for question on games and resolution click here
20.1" TFT has more pixels diods dots hence the cost.
Viewsonic claim "heightens user enjoyment for video editors,fincial traderd, CAD/CAM engineers(that me) and power gamers.
So, like you i would like to see a comparason user test, maybe in next months mag.