Everything depends on your room.
If this is a dedicated theater space, and you have control over the lighting, wall, ceiling, and floor color and you want the most immersive experience, then front projection is the only way to go.
Per the previous poster, the .66 is a designation of the chip size. It is .66 inches in size, which is why it is left off of everything. Texas Instruments has a larger 4K chip and they are coming out with a .47" chip as well this year. The value of the TI chip in the Optoma is that it employs pixel shifting to generate the full 4K resolution which is delivered to it and has reportedly been about the sharpest projector under $5,000 on the market today.
That said, there is much more to consider than resolution. Resolution is about the third or fourth most important thing in a display device. That's why OLED is so hot. Not because it is 4K, but because it can achieve black levels which are far superior to LCD displays currently on the market. It just looks better overall with deep blacks, good motion, and solid shadow detail.
To get this level from a projector (and you better believe that you can!) you need to go to a better Sony unit or a JVC projector. There will be a Sony this year with a native 4K resolution (not pixel shifted) for about $5,000 and it should be stunning. There are also the JVC models which have contrast levels that are unmatched in the industry. JVC employs pixel shifting and will be a touch less sharp than the Optoma, but will outperform it in most other areas. Especially black levels and shadow detail.
The Sony will be a touch weaker than JVC on black levels, but will be sharper, and could be the best looking projector on the market for the year.
Now... In a dedicated room... Why an electric screen? It costs twice as much (or more) for a quality screen and goes down and up for no reason or value at all. Motorized screens are not better than fixed frame screens. They are cooler, but not better. If you want cool, then add some great lighting and some motorized drapes to hide the screen, or a adjustable aspect ratio screen.
With a 16' wide wall, and 19' of depth, you are likely into two rows of seating and a screen size that is easily 133" or larger. That's about four times the size of the OLED displays out there right now. One thing I can tell you is that we love our 64" plasma and it looks better than our front projector, but it's a completely different experience to enjoy the projector. Especially with sports and good movies. It is so much more like being at the theater and being at the game.
OLED, is a nice TV, but at the end of the day, it's just a TV and it doesn't create anything like a 'theater' experience. Home theater starts beyond 100".