HH, It wasn't meant as a slam or to embarass you. I apologize if it came off agressive. I was just amazed that you have that much experience on the board. I'm a newbie here, as you can tell, but I have been reading the DIY screen topics (here and on hometheaterforum) for the last month or so.
I think bcortez answered your question, as did I. I'm not the expert, but since there don't seem to be lots of other answers, I'll give it a shot. The data you provided might change your choice between gray or white. Your PJ puts out a lot of lumens, so the gray should work well, but in a totally light-controlled room, you don't necessarily need the ambient light rejection a gray screen provides.
From my reading, though, I have determined that there are a hundred variations, and they all seem to work pretty well. I have yet to see more than one or two people claim that any solution is THE solution. That's what I meant by "this should be good": I expected dozens of entries giving you alternative experiences. Oh, well.
Here's what I've tried: on the wall (color shift and a little too glossy). White 1/4" foamcore (great color, slight hot-spotting, bad tendency to warp). Foamcore painted with Behr Silverscreen paint, flat black paint surround (much darker blacks, little change in whites, excellent results for about $15, except for the warping). 36x48 pre-stretched artist's canvas painted with two coats SS (same color quality as the foamcore, more rigidity, excellent results for about $30).
Here are the basics: you want a fairly smooth surface on which to paint, and you want a dead flat paint to kill hotspots. With a dark room and a PJ with high contrast, you could just go with flat white paint, and since your PJ is a bright one, SS would give you even better blacks. It's a toss-up, I'd guess.
You can use foamcore (frame or reinforce it, or just attach it to the wall), Gatorboard (foamcore with a harder surface, resists warping), wallboard (some people paint right on the wall). You can stretch fabric (curtain lining "blackout cloth" is a favorite) over a frame (wood, aluminum). You can also buy screen material from many commercial sources.
You can try what I did, or what bcortez or kpatel3 did -- they all work well. You can just paint a rectangle on your wall with SS and outline it with flat black. You can hunt down the forum topics on making aluminum frames and attaching blackout cloth. They all seem to work really well, as well as commercial screens do, according to a lot of people. You are going to have to make some choices, because there's not one single right way. Good luck!
Cherry Hills Driveway Theater