Using Adwords to test Subject Lines
Please excuse this half-formed idea but it may be handy.
Subject lines are well known as a great piece of campaign content to test. Positive changes in this and the FROM email address can greatly increase email message open rates.
Choosing the right subject line, however, can be an area that is difficult to test until you unleash it on your list. But how about taking the learning from any Gooogle adwords campaign you are running on what ads pushing the most clicks and then transering this now tested content directly to the subject line?
In both areas you have minimal space to tell your tale in text and the result you want is the same: a click on.
Maybe worth a go?