I had the Mt700 which is the 7700 clone, it put out a nice picture but let me list the differences as I saw them
1: Mt700 had very bad motion artifacts on pans, ala any hd2+ machine, and while my H78dc3 is vastly better in this area I still see them. Flame suit on
2: I feel the brightness is equivalent, but your eye may "see" the 7700 as brighter due to the elevated black level. I don't feel a 100 IRE field on both units in ECO would prove much different after calibration, but I have no numbers to support this. They both use 250w UHP bulbs and there is no escaping E/I*R so resulting brightness is similar from what I have found.
2.5: Contrast calibrated is ~1400:1 for the 7700 and ~ 2300:1 H78/H79, I thought the 7700 had good black levels until I saw the Optoma, again I think this is why people may find the unit "dim".... it really isn't .... it just has a very low black level that can fool you, once you are used to a higher one.
3: The difference in dithering and noise is no contest, the Optoma has a very smooth almost noise free, refined picture, the 8 seg wheel contributes to a very smooth "green worm" free black. The color saturation difference between them is dramatic as well. The 7700 looks decent, but the Optoma (if not tamed) looks almost wet in the colors. The Optoma has the best saturation I have seen in a digital, but it may be a preference....careful attention must be given here during calibration not to make the picture unrealistic, but the range is there for you if you need it.
4: Optics are not even close, the Optoma has such a better focus ability it allows me to see SD at the same distance and screen size where I saw none on the Mt700...this is a good and bad thing
5: Mt700 was quiet, the Optoma is silent...
6: Creature comforts like lens shift and Motorized Zoom+Focus help install.
Optoma has no presets per input, but memorizes rez/settings by input...not too big of a deal but presets would be nice like the 7700, 3 per input.
No HDMI, the use of a re-pin converter is required
Out of the box the 7700 will render a more accurate picture, the Optoma looks like green fog out of the box....once cal no contest....the finese of the picture is so pleasing.
The remote is a little laggy and cheap in my opinion for a machine of this quality.
Menus on the 7700 were very nice with a very attractive GUI, interface and design. Relocatable popup indicators helped while calibrating.
Menus on the Optoma are cheezy but functional, not more than a days effort for the right coder went into these.
Overall the Optoma is just in a different class. The 7700 and Mt700 were decent but with VAST problems and failures it is dead in the water, and eclipsed in performance by units currently or very shortly shipping.