I don't own a projector, but I was just messing around on the internet after looking at some of the amazing dIY theaters on AVS. I found Carlton Bale's site (just google it) and he has a great excel spread sheet that may help you. Also, Projector Central has some calculators that may work for you. Hope this helps.
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AvFan
Outlaw 976 | ATI 2005 | M&K 850s Left, Center & Right, Surround-55s, MX-70B Sub | Harmony 950 remote | Panamax 5100 | OPPO UDP-203 | LG OLED55B7