for a
"SuperDuper MPG experiment"

wouldn't the octane tolerance of a cylinder head and piston crown combination be more important than any swirl numbers?

I know swirl can improve fast burn,
and fast burn can improve octane tolerance,
but the stuff I have seen
says that 'old fashioned' quench area works better
but that modern cylinder heads have had to cut
back on quench area due to pollution concerns related to NOx

Porsche engineer May's HE "Fireball" high quench area head for Jaguar's V12:
http://www.jagweb.com/jagworld/v12-engine/page3.html

Larry Widmer's 'Soft Head' article (aka TOO or "The Old One")

http://www.theoldone.com/articles/The_Soft_Head_1999/

the Aussie view of pinging & detonation:

http://autospeed.com/cms/A_0601/article.html