I created some multiplayer games with AI players and ran them for a while, here are the results.
ancient sun of fire: 40x for 5 minutes
impact: 65x for 5 minutes (at which point the yellow player taken over the entire map)
Noticed no problems.
ancient sun of fire: 30x. After less than a minute I had to decrease the speed to less than 10x.
impact: 30x. After less than a minute I had to decrease the speed, and then I think it froze completely.
In both the r6066 games I noticed lots of messages like 7: building road, immovable in the way, type=7 printed in the terminal, but I don't know if they are related.
>I have no idea if this is related to the blocking stones in the middle or the water area around.
I don't think so. I first noticed it when playing a game on "Three warriors" which is a lot more open.