Well, you have a wealth of Lumens. (3600) You stated that you absolutely did not want to chance seeing a single 'sparkly" or trace of Graininess.
Of them all,a Silver Fire 5.0 can allow you the most leeway as far as ambient light performance, but if your Eagle-Eyed" (20/10), the metallic content that allows for a darker Gray to provide a brilliant image with dynamic looking Whites might manifest itself too much for your personal taste.
So if you place the Optoma within 20 % of it's minimum Throw distance (12.8'), and run the Optoma on Normal Lamp, driving into a 7.5 Neutral Gray, and have calibrated the PJ to optimally utilize the Gray surface, you should a a very clear, "open window-like" image with impressive Blacks, and excellent whites.
Of course, in a comparison to a true White Surface, or a metallic infused Gray surface, you'd see the difference immediately as far as gain and white levels are concerned. (...and the white would perform miserably in ambient....) But if you do not make such a comparison, most everybody on this Planet who needs ambient light watching ability and/or help with a bright PJ's lack of Contrast range, and has done a smooth, error free Gray surface that was getting blasted with mega lumens will vouchsafe that it's never something anyone can...or will notice on it's own.