It was not clear which of the PI distros you are running in the Rraspberry, but I believe it is not bare metal, and even if it were based on Linux OS, certain latency is expected in the execution of the Python commands, since several other processes will be running in the sequence. Keep in mind that operating systems do not deal well with processes with high update rate; in such cases it would be necessary to make use of some kind of hardware interruption in order to promote the desired process to a higher priority level. Also, you did not inform to where the Print output is being directed (serial ?, console?) , which depending on the case could generate an additional delay; note that each float value has a different amount of bytes to be sent. By the way, the aerial wiring you did is not adequate to handle I2C bus, put the shield as close as possible of the main board and wirings shortest.