OP, as others have said, rangento a repeater is a different issue, as most are high as possible, giving you good LOS. I can easily hit repeaters 25 miles away with stock antenna on any 5 watt ht from where I'm at.
Simplex range is different, as both stations most likely neither station will have great height AGL. Terrain dictates, depends on signal path obstructions.
This is timely, as we continue to test this, and yesterday achieved 5 miles simplex, between a Baofeng UV-82, and TYT MD-UV380, both equipped with Nagoya 771 antennas. Would not have been possible with stock antennas.
This is relatively flat ground, with trees and 1 & 2 story buildings in between. Not heavy urban, but not completely unobstructed. Was pretty cool.
Again, on 70cm. Tried on 2m, NO-GO till about the 3 mile mark. UHF is getting through and around the obstacles better.
A good 1/4 wave antenna may have you hitting repeaters 30-35 miles away. A roll up slim jim (or other big antenna) high up can have you hitting them 47 miles away, in my experience.