Just to add on here, doesn't the A/B test in the Email Program have the same functionality if you select the Test Sample Size to 100%? Marketo automatically does the random sample for 50% to receive email A and 50% to receive email B. The "winner" is determined but of course you do not have to send the winning email.
[EDIT]
It works, I'd suggest this method instead as the reporting is done for you.
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