Yes the cloud limits you to 1 update per second (or 4 per second in short bursts) as you have seen.
One option would be to make your photon be a TCP server (listens for connections, when connected sends the IMU data every 1/60th of a second). The TCPServer documentation will have an example of this.
Another option would be to have your computer act as the server and have the Photon open a connection and send the data. This recent thread Quickest way to stream data from Photon has examples of this.