We recommend no more than 24:1. Many experienced builders don't run a 'break-in' mix but start out with whatever they plan to run. You'll find many go to 32:1 and stay there.
Some of the synthetics are formulated to run at as low as 50:1 and a few, Opti-2 for example is mixed at 100:1.
You'll also find those who say not to break in an engine on synthetics because the theory is the rings take longer to seat. Or won't seat at all. The jury is still out on that one.
Maybe use the search feature, type in 'oil mixture' and you'll have plenty to read and get lots of opinions on this subject. http://www.google.com/cse?cx=partner...ure&gsc.page=1