Understanding utilization and credit limits.

Most professionals would tell you to keep your utilization below 20-30%. Anything higher than that will began to affect your credit score significantly. The higher your utilization, the more your credit score will decrease, regardless of good payment history.  

If  you have several different credit cards with different utilizations, and you purchase a tradeline, it may not help your score at all depending on the utilization ratio of each credit card.  Your overall utilization may equal 30% with adding a tradeline but each individual card with high utilization will still affect your credit score. The logical thing to do is to be sure you have low utilization on your current credit cards before purchasing a tradeline to ensure you get the most out of the tradeline. 

There are a number of upsides to having high credit limits or increasing your credit limit on your credit cards. Increasing your credit limit can lower credit utilization, potentially boosting your credit score, thus improving your credit. However, if an increase in a credit limit encourages you to spend beyond your means, the mounting debt will likely outweigh any benefits. Think carefully before raising your credit limit.