Calculations for projector mounting

 OK - New projector - first ever to be a ceiling mount for me.  I once found a site that had the calculations for how much ceiling drop to use on what size screen to avoid keystone correction.  Haven't been able to find it since (yes, yes, I KNOW I should have bookmarked it...).  Any'a youse gals know where I can find that info?  
Also, are mounts projector/make/model specific, or should I just go for a "universal" and be done?
Finally, is there any difference in setup quality between the DVD disc & a blu-ray version?  This projector'll start life with a DVD source, but (when the budget allows) step up to an Oppo B-Ray model.  If calibration is calibration, then I won't need to invest in the new calibration disc.  If there are additional tools I need to learn on the B-Ray, then I'll choke up the $$$.
Thanks - Boomzilla