Uhm... It was. Titan and others did lots of such testing. It is in fact how we know under-volting is even possible, and that the MPU "sweet spot" is around 500Mhz.

Whoh there! Hold on a second. One quick question: How long did each test run for? And how much longer did the under-clocked test run? Also, where you writing said file to flash? If so, you're not testing MPU, you're testing flash write, since that's by far more expensive than the MPU running. And if you're not counting the extra idle time the system has after the faster version is done, it's not exactly a fair test. the whole concept of race to idle means you need to count that idle time as part of the equation.

What you would ideally do for real MPU test is run an app that pulls it's info from /dev/random and pushes it's output to /dev/null, or something like a pi generator. Then find out it's maximum run time (should be the slower clocking), and have it run several times over a set time frame. Something like this would be great:

Now, if you have the line above and it takes 10 second to run on stock, have it run the app every 30 seconds for about 30 minutes. Then do the same on the overclocked device, in exactly the same time frame (30 mins). The important thing here is that it should run the app the same number of times in the same time interval. And that interval has to be reasonably long enough to be a real test... a few seconds won't do. In this example it should run the app 60 times, roughly distributed, over 30 minutes.

All other things being equal, I'm willing to bet that a device clocked at 500-900 will have much better savings than one clocked at 250-600 (from my own experience). This would be the "race to idle" effect showing itself. (Btw, this test has been done several times in multiple threads with the same results: OC == better results.)