At your size you could get the FlexiGrey around $65 which should give a similar picture with a slight increase to brightness and possibly a slight improvment for blacks if the screen's color is visibly darker than the paint when the projector is off.
The Carl's ALR for around $125 should give an equal or larger increase to brightness as the FlexiGrey when seated relatively near the middle while also giving a much more noticeable improvement for fighting against the nearby wall and ceiling reflections AND better fighting lights that hit it from an angle.
If you're thinking about spending the money for a screen material and want a visible improvement to make it feel worth it, I'd suggest spending the extra for the CarlsALR instead of the FlexiGrey..it'll be a much bigger difference while costing less than any other ALR material available.
As far as paint options, the fact that a nice flat-grey is working for you along with that screen-size is a nice benefit..it means you could easily go with something of modest to low gain and still keep similar brightness as you're seeing now while getting less washout from the nearby wall and ceiling reflections. The main problem is that flat-grey is basically invisible while projected upon EVEN if the painting didn't go particularly well, while a more aggressive light-rejecting paint mix will show more and more imperfections in the surface and paintjob with the more aggressive the mix is tuned to be.
You could probably get away with a pretty well-behaved paintmix because of your screen-size (something like a half'n'half mix of RalphLauren/DisneyGlidden tintable metallic "untinted" mixed with flat interior paint tinted "Seal Grey"... or the lighter 1.5parts metallic and 1part "Seal Grey"), BUT an even easier, cheaper, and more assured way of getting an improved image is leaving your perfectly working screen alone and simply hanging some dark cloth or putting up a dark curtain on the wall next to the screen and considering pinning up some dark material (or dark paint) on the ceiling above the screen. This will take care of the reflections without costing more than about $20 and there's basically nothing to worry about messing up.
Last edited by Ftoast; 02-16-2016 at 08:15 AM.