Benq w7000 has adjustable IRIS in service mode so you can 100% control how dark it goes, you can make it go all the way down to pitch black, and it can be controlled in 100 steps. It is also overall the sharpest under $2200 projector there is, you can get refurb ones for around $1600 and they still come with a 1yr warranty.
I think it's a simple answer, Benq w7000 for sure. You absolutely have to make sure you get one with 1.03 firmware, otherwise it won't be as sharp for text.
Although I personally find using a projector as a monitor slightly awkward, but if you make a special seating area and get it right, then it could be ok. Possibly put a desk in front of the screen and it would work.
I used a desk before in front of a projector and it is better than doing it from the couch, eventually couch posture causes problems. The Benq w7000's text is sharp enough to use like a monitor, but it will still cause more eye fatigue than an LCD, although it's very bareable for long-term use and if you have a desk for good posture should be fine.