I've searched in DAL and googled and am trying to how fast data will get
to the bus from a typical 7200 rpm or 10000 rpm hard drive (ATA) vs. a 20x
DVD drive (also ATA). Obviously, if they're both on ATA on an older pc that
will limit any difference in read speeds ...

Thinking of burning a volume to DVD, changing how an appl. is addressed
and running it from the DVD. Does anyone know if this sounds smart?

If I do this for games running off the CD-rom and read it's installed files from
DVD would I gain anything over just getting installed files off a hard drive?
Other than the flexibility of using the DVD?

You would lose a lot of performance and loading delays will become severe due to the fact that CD/DVD seek speeds are very bad compared to a hard drive. There probably isn't a game that will read each file contiguously as that would become a boring game. Most games today are all played differently by everyone whatever you do in the game, it has to read from the CD, multiple files probably, and read speeds of CDs/DVDs are mediocre compared to Hard Drives (in my experience).

Bottom line, playing games off a DVD will not get you performance increase, more likely a decrease.