To protect the platform and experience of users, rate limiting is imposed on the use of the Ethfinex APIs. These limits are dynamically calculated based on a user's trading volume.
The base limit per-user is 1,000 orders per 5 minute interval, and is shared between all account API connections. It increases proportionally to your trade volume based on the following formula:
1000 + (TOTAL_PAIRS_PLATFORM * 60 * 5) / (250000000 / USER_VOL_LAST_30d)
Where TOTAL_PAIRS_PLATFORM is the number of pairs shared between Ethfinex and Bitfinex (currently ~101) and USER_VOL_LAST_30d is in USD.
Using this formula, as your trading volume increases your API limit also increases to accommodate for placing a greater number of orders and cancels per second.