I don't think there are any rigid rules, although the average seems to be a 6" overhang. For example, a 60" runner was once recommended to me for a 48" table, and a 72" runner for a 60" table. That would be 6" for each side. Some people seem to prefer 8" or 10". There are also some that are meant to sit on the table top and don't hang over the side. So it seems that you can choose your own "hangover" : )

I have a friend who leaves the runner on when she extends the table and the runner doesn't reach out to the edge of the table. But she can decorate it in a way that will make it work.

I do not have a photo but mine goes over the edge about 10-12 inches on each side. So I would think 120 inches would look good on your table.

So does it look better to have it hang over if it's pointed with the tassel on the end and if the end is squared it could more easily not reach the end?

When they are pointed with tassel I like them to hang over. If the squared off doesn't hang over I like it shorted and not to the end of table, somewhere around 2/3's of table. I don't know if there is any rules tho.