I first scale the video to the resolution of the HMD I'm trying to simulate and have the rest of the screen displaying black, I then measure the diagonal size of the image and using the formula
viewer distance = (screenwidth)/(2*tan(FOV/2))
put my eye at that distance from the screen. I'm pretty sure this gives a reasonable idea of how a specific HMD will appear.
So, for example, the Zeiss Cinemizer has a FoV of 30 degrees and a resolution of 870x500 which is a diagonal size of 25cm when displayed natively on my monitor. 25/(2*tan(15)) = 46.7 cm viewing distance. What this has shown me is that I find 30 degrees to be quite comfortable for viewing movies and that much more than 45 becomes uncomfortable.
Funnily enough, I found this quote from Zeiss which might explain their choice of FoV and intended audience when doing research I think the bit about resolution and ppi is a bit of a cop out though:
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Hi Anchal, imagine sitting in the front row of a theatre: In order to see everything that is happening on screen, you would have to keep moving your eyes and head around constantly. The reason why we decided on a 30 degrees field of view wi
th the cinemizer OLED is that we want to offer its users a maximum level of comfort - without them having to strain their eyes. :) Many people who were not able to try the cinemizer OLED themselves yet are sceptical at first when they read about the resolution of 870 x 500 pixels. However: That's the resolution of each of the two displays, which also offer a pixel density of 2500 ppi. At this year's CeBIT, thousands of visitors experienced the cinemizer OLED for the very first time and - despite the occasional scepticism - were absolutely convinced afterwards. To cut a long story short: Give the cinemizer OLED a try! Maybe at the IFA 2012 in August! :)