Significant lagging with Sony HMZ-T2

[Sven]

Hi,

we were using Vizard 3.0 with a NVIS SX60 HMD and an Intersense 900 Tracker. This worked ok. Recently the NVIS broke, and we are at the moment looking into replacing it with a Sony HMZ-T2. However, we are experiencing significant lagging during head-turns. Is this caused by the graphics card? With the NVIS, we used a nVidia Quadro FX3700. As the Sony needs HDMI input, we are at the moment using a low-budget Radeon HD 6450.
Does anybody know if the lagging can be reduced with a better graphics card? Or is this caused by th Sony HMD and cannot be remedied?