How about playing a double round robin afterwards with these 6 or even the best 8 engines, but without any opening book? No more arbitrary opening choices, but the need for each engine to show its chess understanding from the first move.

As the "best first moves" of these engines all slightly ...

Thank you very much for Gull. I have one request: Pondering does not work at the moment. At least for me with Arena GUI. I always play my engine tournaments with ponder on. But Gull only thinks when it on the move, thereby using only 50% of its processor time.