It may help to know that most prototyping board places (cheap low quantity board fabrication from china) say a low limit of 6mil spaces and 6 mil traces but they prefer 8mil spaces and traces. Once you go to pro boards (4 layer plus) you can go down to 2mil but they again prefer 4mil.
I have my DRC set to 8mil and will go to 7mil when I have no other choice.