i2c standard:
"This depends on the load of the bus and the speed you run at. In typical applications, the length is a few meters (9-12ft). The maximum capacitive load has been specified (see also the electrical Spec's in the I2C FAQ). Another thing to be taken into account is the amount of noise picked up by long cabling."
Note that the old PS2 computer Mouse and Keyboard uses i2c. The Nintendo Wii Nunchuk uses i2c so cabling is appropriate to use.
note that the GY-521 requires a 5V power supply and also note that the i2c Buss has 2 4.7k ohm resistors pulling the i2c lines to the 3.3V side of the onboard voltage regulator.
So using additional pullups will only complicate things.
Z