I'll second 40:1 as the ideal if you're keeping oil injection. Now that I know how the injection pump works, it's definitely not linear, so it's lean at times and rich at other times... Keeping the lean times from being too lean is pretty important.
My M8 is an oil piggy at about 25:1. I'm making half turn adjustments to the rod between fills to get it closer to 40:1.
My '04 600 was ~40:1 from the factory and ran great, but melted a hole in one piston under warranty. Dealer rebuilt it and set the oil to 30:1. He said it was probably a slug of bad gas or water, but extra oil would help... I figured oil was cheaper than another rebuild and left it alone for the next 4000 miles, but had to clean the power valves a lot...