I have decided to go for Da-Lite, but now i have more questions.
Who would have thought that selecting a screen would be that complicated, well, not me

The place where i am thinking of placing the screen is at the picture.
Its 12'5" (149") wide and 8'4" (98") high.

First:
The reason i started this thread was to ask weather the side columns will reflect the light on a disturbing level if i go for the planned Cosmopolitan Electrol 65"x116" screen (to use with epson TW5500, aka 8350), which will be a little more than 1feet farther from each wall.
If the answer is "yes definitely" than i may go for a smaller size (58" x 104") which will give almost 2feet from each side.
But the price difference is so little i want to get the bigger one, and put black pull-down curtains on the side columns as you have mentined.
But it will not look nice.
However, considering my viewing distance is 16'4", do you think 65"x116" will be too big?
If it is, i can always rescale the image for a smaller size but than, i think, the rest of the white screen will reflect and disturb me, as i can not benefit from the black borders.
In that sense, is it bigger is better?
Second:
As it is not a dedicated room, i do not have light control, however i will usually watch at night with lights closed, but the room never gets pitch black, i mean you do not need a flashlight to walk.
Imagine the brightness as the light from the moon in a room with light colored curtains (veil?) closed.
Is this situation, considered as a bright room in projector terminology and i have to go for high contrast matte white from da-lite or standard matte white will do?
Or do i have to go for something with more gain, like gray?
Third:
Considering the screen will be used at home, maybe 3 days a week (in the beginning and getting less use after time) and will be closed while not watching, do you think paying exactly twice as much for tension is a must?
thank you...