In order to take down the 250 base you will either need to have level 6 warp gate or be around level 80 attack and health. This means you will need to have a attack and health of around 800% bonus to take down this base successfully. This is not to say you cant do it with a lower bonus just that it wont come so easy.
I would recommend having a EXP boost on when attacking this base because it will give you a lot of exp just for the attempt which can level you up quickly and give back the warps if you don't succeed in taking it down.
Another recommendation would be to have your max resource captivity around 10 million or more to hold the resources you will get from the attack and levels gained. Also make sure you have a surplus of Spectors units because you will lose a lot in these attempts.