All things considered, the Rosco TV paint is pretty basic stuff that really offers little real advantage, especially in your situation. A Basic Grey simply attenuates "all light" and only lowers the black floor by virtue of the Grey tint itself.
In other words, it's almost like your throwing your image through a N-Filter. Your just turning down the vibrant aspects that come with 1.0> Gain like using the Brightness control.
So going elsewhere............
Do not discount the amount of Contrast boosting, deeper blacks, vibrant colors, and ambient light resistance you can get from a light to mid-shaded to darker shade of metallic infused Grey Paint "Mix"...and still stay at 1.0 Gain. (...w/no hot spotting...)
Silver Fire using no colorant is a overachiever but adding 3 oz of colorant will make everything do even better when dealing with higher levels of ambient light.
Flexi-Grey? Not remotely close to Silver Fire in every respect except not having to paint. Even so, it's always a case of optimizing the Projectors Lumen output with the screen size and Throw whenever you want to get the best possible results in ambient light.
Panasonic PT:AE8000u @ 16.5' Throw onto 140" diagonal with plenty of ambient light. Silver Fire v2.5 4.0
The entire end wall is painted in Silver Fire, and you'll note how intensely black the non-illuminated area surrounding the Image is. Therein lies the difference...if your screen is truly a hih Contrast surface that can maintain gain. Weak light gets attenuated. Intense light stays intense.
Now be advised that if you keep Window Shades / Curtains flung open at Noon, with sunlight flooding the screen area, while you image will be significantly better than almost anything else, your image quality will still take a hit. You'd have to drastically reduce your screen size (98" diag.)
By simply keeping any light from directly hitting the screen, you can realize some great image quality. When I see someone state that they have uncontrollable light coming from Window at the side of the Screen, I start to wonder how seriously that person is taking having "The Big Picture". Even thin, Gossamer-Style curtains in a Grey would make a tremendous difference. Frankly, if you've never tried at least modestly correcting your worst case light sources, you cannot appreciate how even small efforts can make big differences. As I said above...we / you can make it look a LOT better than you have had to settle for, but you'll still have to settle for something less than a perfect OMG level of image quality.
So dissecting your situation....first thing that comes up is getting the Format sizes right.
At 16:9 and 100" x 56" you'd have 115" diagonal with a 4' Throw...and with Silver Fire v2.5 4.0 you'd get 35 fl of reflected brightness. Light uniformity is well above 85% so no dark edges.
Here is a Link to a Thread where a ViewSonic PJD6683ws 3000 lumen Short Throw Projector was employed on a 106" diagonal Electric Tab Tension Screen painted
with Silver Fire v.2.0 4.0
Again....lots of ambient light...and dozens of examples to look at...from all sorts of angles at different levels of room illumination. It is amazing how bright a room can be as long as your not washing the screen surface with direct light.
A sneak peek:
You have to decide how good you want your image to be.There are no miracles...but there are some applications that work a lot better than others.