Tier III
The six had all taken the evolution challenge, which was surprisingly easy this time around as it only needed them to take down a Tier III being this time, only one.
It was only when they found a weak Tier III monster to fight that they realized that the challenge was not easy at all. The more powerful one became, the bigger the difference between Tiers, except for the first two where the second actually gave a bit less of a bonus compared to the first.
The third, fourth, and following evolutions didn't exactly double the stats, but at that point, the stats that they had would be so high that even an increase of 10% would be a noticeable boost, not to mention more.
It was their base stats that would improve, which meant that the bonuses they would get from the items would be higher as well, making the total increase in power even more than double.