Testing Specials for Soy Wax Candles

I'm sure somewhere there is information on what works better as far as specials go. But for me, I like to test things out for myself. So what I did was send out the special to several lists and posted to several places. I sent out two different specials to see which one is responded to is better, and then different codes for each list/group/board to see which one has the best response. I used the two following specials:

Free Shipping: FREE208040020
10% Off: DISC108040020

This will be an on going project, and I'll most likely be testing this for several months.