So to clarify, what you want to quantify is the real-world power efficiency of an uncleated cycling shoe with moderately-snug toestraps & toeclips, as it compares to a typical touring-compatible clipless setup like SPD with touring/mountain shoes? That won't be easy to find a study for, I don't think tourists care enough to install a PowerTap and start measuring that type of thing. Even Bicycle Quarterly's PBP report (PDF) doesn't bother touching on pedal type, despite delving into esoterica like what style of fenders people used.

If you can borrow a PowerTap-equipped wheel and a Garmin Edge 500, you could always do your own fact-finding on the subject. And that would probably be best, since some aspects of the subject would be rather individual... for example, I'm a high-torque, low-RPM type of guy, and at 280 watts on a hard climb, I would probably pull my feet out of your toeclip setup the way you run it.