Every time there is a question hanging in the air people call for A/B tests to find out the right solution. Isn't that a bit lazy? You don't have the time to test out everything with A/B tests, considering they aren't as easy to do as you think.
My answer is always do what best practice is from successful online games. So you simply take a bunch of them and look how they do it. Most of the long running ones have tested the hell out of their systems, so why don't you take their lesson and simply steal their key findings? They have it right there for you, online, in their game.
So there was a question recently if its better to sort your premium currency packages low to high or high to low. The answer is now really obvious if you follow my advice. You don't need to run an A/B test to find out.
You can learn so much by looking at good f2p games and what they do. Some of them even have fan made statistic sites which you can use how successful they are in various countries, popular items or vehicles. Simply look for them.
So open your eyes. All knowledge is right there in front of you, a simple search away.