Steven,
The purpose of a headline is to get your readers attention so they read the first paragraph, then the rest of your offer. Now just getting their attention isn't going to do it, you need to build desire (or at least some interest) in reading the rest of the page.
Both
Ted Nicholas and
Dan Kennedy are right in the length of a headline, as long as it connects with your target buyer. That
connection means more than the number of words. When I'm writing copy for clients, I build a huge list of headlines around the offer.
From this list I can do some testing in
Google Adwords, with banner ads, or other direct links to see which headline gives me the best click-through. This tells me where to start. Another idea to test headlines is run them in a post card lead generation or small display advertisements.
The bottom line is you're going to need to test your headlines. In some markets a fear of loss headline will out pull a curiosity headline. On the
AdBriefing's Patrick Quinn talks about
Writing Commonsense Headlines, you'll know for sure with a little practice and testing.
You are right to
test headlines first, this is critical because if you don't get your readers attention then they can't read the rest of your offer. I've outlined the testing methods I use and find effective, you'll also want to A/B split at your offer letter (or mail tests in series.)
Best,
Justin