I was actually thinking about doing Black Flame and buying the premixed paints from PB-maxx and MM's new side business : http://xtreme-fusion-screens.com/
My reasoning was that the loft is totally uncontrolled and is quite bright during most of the day. I actually bought the Formica planning to use it as a substrate for painting, but now I have it mounted I am noticing that (a) I wouldn't really want the image to be much darker, and (b) most of my movie watching is after the sun goes down anyways.
Having said that, going to something like RS/MM is probably the right thing to do. I have a huge light splashback problem with the angled walls "above" the screen, so there is still a good chance that a darker screen would give me a better overall result. I have to admit I am surprised how good the image looks on untreated Formica, so the last few days have been spent worrying more about what form factor (2.35:1 or 16:9) to use rather than worrying about paint.
BTW, after much soul searching I have slipped back to a 1.85/16:9-ish aspect ratio for now. Per my own decision table (posted yesterday), I am DEFINITELY going to end up with an anamorphic lens but I am not sure I'm willing to put up with all the zooming and shifting required to make best use of a 2.35 screen before the lens appears in budget.
I need a chainsaw, a trailer, and a land survey more than I need an anamorphic lens/prism, unfortunately. Guess I will just match the aspect ratio of the "bars and all" projected image for now, whatever that happens to be.
EDIT -- "Tiddler" has posted some really good "advanced rolling instructions" on avsforum which, if followed, seem to be sufficient for a beginner to reliably apply RS/MM and get good results.
I checked yesterday and it does appear that a paint/poly/pearl mix like you were considering is still easier to apply because of the lower metallic content. I should also mention that the criticism of Silverscreen is only really saying "grey paint mixed with poly and pearl makes a great screen, it's just that Silverscreen is a bit too blue; you can get more neutral colours just as easily". RS/MM does seem to give a bit brighter image at the same "greyness" level due to the metallic content, however.