By default, the Beyondcoin Pool will adjust the difficulty of your miner automatically over time until you have from 5 to 15 submits per minute. It's a good trade off between bandwidth and accuracy.
You can also set a fixed custom difficulty using the password parameter. For example, if you want to set the difficulty to 64, you would use:
-o stratum+tcp://beyondcoinpool.com:3433 -u wallet_adress -p d=64
Here are the accepted values for the custom diff:
Scrypt: from 2 to 65536
If the difficulty is set higher than the current difficulty of the stratum, it will be forced down to fit Beyondcoin's current difficulty.