I'm still pretty new to the hobby (at least GMRS I've been
talking on 11 meter CB for many years) but here is what I've
learned in the past year. I have 2 brothers. As the crow flies,
Brother 2 lives 4.5 miles away and Brother 1 is 3 miles. CB is sporadic.
Sometimes very difficult to hear because of a lot of noise and, of course, you
have to 200 watters trying to outdo each other. So, we often
find ourselves switching channels to get away from the loud
noise level.
GMRS on the other hand, I can talk to brother 1 who is 3 miles
away on simplex most of the time. Brother 2, who is 4.5 miles
away is much more difficult on simplex, but most definitely easier
when using a repeater. Keep in mind. They are both using small
Baofeng 8 watt handheld radios. Brother 1 got a mobile radio
and a 1/4 wave antenna about 15 feet up. He and I talk easily
on simplex whether I am in my car or on my shack radio. Repeater
talk is as clear as using a telephone.