I too mail to similar list in the same areas you're mailing. I mail Cherokee, Cobb, and North Fulton (6 zip codes). Absentee owners, and Owner Occ 50+% equity & 55+ age with some last market sale date, bedroom/bath criteria, and age of home criteria. I have mailed that list twice now of around 2,000 mailers and got 12-13 calls the first go round and about 15 calls the 2nd round (still getting a few trickle in). Mostly "take me off your list" and the rest just kicking tires and want top dollar for their property. No deals the first round, I might have a deal on this 2nd round of mailers. I'm going to order round 3 next week so it hits the mail after the new year.
when I first started doing direct mail back in May, I mailed a similar small list of around 300 highly targeted absentee owners and I didn't get a deal until the 2nd mailer of that. Only had about 5-6 calls per mailer.
There's just a TON of people doing direct mail right now in the Atlanta Metro area.
I will keep mailing this list, but I'm starting to work on my web presence with social media posts & blog posts to boost SEO, and about to start an adwords campaign as well. I'm also posting CL ads, networking with wholesalers, and browsing the MLS daily and making offers on properties with certain keywords and high DOM.