No worries, I found it helpful and thought you might too. Before stumbling on that, I didn't appreciate some of the trade-offs involved with gain, for example. Or the different performance a given screen might have with on-axis versus off-axis gain. Or color neutrality of product A versus product B. Jeff's report gave me a place to start.
Most are proprietary.
You will have more fun, and get a better result, if you do some more reading one rainy afternoon. After 3 hours of study, you'll know more about projector screen performance and tradeoffs than 99.9% of the human race will ever know. Otherwise, if you just ask 10 people what to do, you're almost certain to get 10 different answers, leaving you feeling ... a lot like you feel right now.
Individual opinions don't count for much, but since you insist: You say that you'll be watching with a window shade open or a light on sometimes. Based on that fact, one thing that jumps out at me is that you'll need gain.
I am in a similarly sized room as yours, but there are no windows, totally enclosed HT. Even so, I ended up with 1.4 gain, and it is not too much. It's just about perfect for me. I can run the projector in Eco mode constantly, which is huge because I don't want to hear the fan. It would drive me nuts (more than it would most people, since these are fairly quiet pj's) if it had to be running high all the time. But that's just me.
You already know the things that matter to you. You have opinions. You may be a nut for color neutrality. You may prefer really bold, dialed-up color. You may want a super bright screen. None of us know any of that. You may not care if the fan runs on high. All of that is personal preference. Do some reading, learn what some of the trade-offs will be, and think about it. You'll be much happier with your final result.
Think of it this way. You are going to watch thousands of hours of movies and football on this screen. Do yourself a favor, sit down this weekend, and just do 3 hours of research on screen performance. After you do that, you'll probably decide that you need to do a little more, just to answer the new questions that you've raised. Perfect. That will mean you are where you need to be.
If he is a true dealer, he will have access to all of their surfaces.
This is the link from Jeff Meier at AccuCal, for anyone else interested in his excellent (IMHO) screen fabric report:
Good luck Herm.