A regular CAT5 RJ45 has 4 twisted pairs, but they're not "in order"

1,2 orange,orange/wht
3,6 green,green/wht
4,5 blue,blue/wht
7,8 brown,brown/wht

I'd pair the SDA and SCL signals each with a GND (ie 1=GND, 2=SDA, and 7=SCL, 8=GND) and use the others for PWR/GND.

10 meters is a long way for a single-ended TTL level signal. They make I2C bus extenders for this sort of thing.