I've run CAT6 throughout my house, mostly in the basement where the TV area and office are. I have a cable that goes upstairs to my bedroom along the chimney from the basement to feed a wireless access point. There are 3 spots where the cable comes about 4-6 inches away from electrical wires. The power and ethernet wires are parallel for about 18" and about 4" away from each other. Will this make an impact on my data signal?
CAT6, even "unshielded", is very resistant to electrical interference, just as it can carry very high-speed data while emitting little or no interference. Plus, your power cables have pairs of conductors carrying current in opposite directions, so any interference they emit is going to rapidly diminish with distance.
(For fun, here is an explanation of how CatX cables reduce crosstalk and increase EMI resistance.)
In real terms, 4" is plenty of spacing, even if you ran the two lines parallel for much longer distances.