If your worried about eyestrain when viewing 3D. The thing to do is look at the refresh rate (shutter speed) of the eyewear and projector.
Usually a TV's eyewear has a refresh rate of 120Hz,
Many projectors eyewear seems to be around 240Hz. Othes have a quicke refresh rates which range from 480Hz to 720Hz.
As far as I can see with projectors, you get less eyestrain that you get with a TV as the refresh rate (shutter speed) usually twice the speed. The environment also has a contributory factor as room is usually darker when we view a projector. This limits the surround light, which is where your eyes gain the strain from.
But also remember that everyone is different and demoing is still the best option.
I would agree an 8hr dem would be a killer dem and would beat my 5hr demo I did with an AVForums member sometime ago when he wished to carry out a shoot-out review for the AVForums on all our projectors. If you are bothered by this, then the simple rule is the quicker the refresh rate (shutter speed), the less eyestrain. 240Hz seems to be comfortable for most people, which means that almost every projector will be fine.
Regards, Shane.