I don't know if they do samples. But I'm about to have a whole lot of extra 2.4 material
But to answer your question I think it depends on size. I got around to playing with the settings on my projector and the 2.4 gain is perfect. I think that at the same size the 1.8 would've killed the whites. Let me say this plainly: My blacks are just fine with the 2.4 white.
I think you should do the math to get fL and see what kind of number you get. I think if you are near 16 with the 1.8 grey you should be okay.
fL=lumens times gain then divided by the square feet of your image area
Of course the main assumptions you have to make is how many calibrated lumens your projector puts out. I am (assuming) I am getting (based on reviews) 450 lumens. So with the 2.4 white I am about 20 fL. With the grey I'd be at 15 fL. The wall was giving me around 8 fL
Then there would be the reduction in brightness for off axis viewing. Which, I am guessing is easily 15%
I then took into account that I want to use the lamp in economic mode to extend it's life and I ddi want to turn some lights on.
All that to say that while I initially thought I wanted the grey, the white made more sense to my application.
All that to bring me back to a question "What size screen are you thinking of getting and with which projector and
are you going to change projectors in the near future?"