I feel like there two things that should be A/B test here: 1) Best length of trial to get someone to sign-up for a free trial 2) Best length of trial to get so

I feel like there two things that should be A/B test here: 1) Best length of trial to get someone to sign-up for a free trial 2) Best length of trial to get someone to convert to paid user. Your actual conversion is going to be a combination of those two factors.