just like the interstate hwy. low traffic (fewer neighbors per node) and you can speed through with lower latency numbers. once they get home and midgete porn viewing begins, congestion begins
with fiber the efficiency can improve drastically and it is usually not encumbered by neighbohood traffic issues
still, it comes down to the design of the service provider's infrastructure.
I have $65/mo FIOS via Centurylink and for the past 3 years, it has been consistenly, day after day, regardless of hour...provided me with 900mbps+
you may want to try reading reports from subscribers in your area for the companies which service there and see what they have to say...away from the hard sell advertising of the company. there are online cable compaint forums as well