How does i2c standard or fast mode effect the output data rate of the sensor?
They are completely unrelated. How fast you read the data does not change how often the device samples or updates the internal registers.

The reason for choosing 100 kHz or 400 kHz I2C has more to do with how fast you want to drive the bus, which in turn determines your required pull-up resistors depending on the length of the bus, number of other components, amount of data to transfer, etc.