the 1200 feet per minute piston speed
come strictly from experiments
... no theory to it, just many many dyno tests of brake specific fuel consumption (BSFC)

this book has a good graph showing fuel economy by piston speed and manifold pressure
near page 378:

http://www.amazon.com/gp/offer-listing/0262700271/ref=lp_g_2

or

http://www.amazon.com/gp/product/0262700271/ref=olp_product_details?ie=UTF8&me=&seller=

repeating for emphasis
you can create engines that get maximum fuel economy above 1200 fpm,
but only if you use
special bore coatings (ceramics),
special rings (very thin & hard),
etc

or "chop the Gordian Knot instead"
and do away with
rings altogether

http://www.newscientist.com/article.ns?id=dn8658