another important thing when i test a product on several sites and the payout of the product is lets say 9$ , i will put budget of 2x =18$
and spread evenly, if i see some sign that it may work i continue to check if not i drop this site. sow if my cpm is 0.50$=1000, sow the test for this will be 18$ that it 36000 impression for test, and the time also very very important..sow your ad start to appear only from the hours that most of the people at home and not in the work.
for people that print money better to go with high payout if the cpm on some site is high.