Changes to the network interface and a small processor revision sound minor but could make a difference for your project.
Raspberry Pi 4 vs Raspberry Pi 3B+ — The MagPi magazine
Raspberry Pi 3 Model B-Plus – Full Review and Benchmarks
Raspberry Pi 4 vs Raspberry Pi 3B+ — The MagPi magazine
Raspberry Pi 3 Model B+ is the latest product in the Raspberry Pi 3 range, boasting a 64-bit quad core processor running at 1.4GHz, dual-band 2.4GHz and 5GHz wireless LAN, Bluetooth 4.2/BLE, faster Ethernet, and PoE capability via a separate PoE HAT. 5V/2.5A DC power input.
Raspberry Pi 3 Model B+ SC0073
Raspberry Pi 4 vs Raspberry Pi 3B+ — The MagPi magazine
Introducing the Raspberry Pi 3 B+ Single Board Computer - Raspberry Pi Spy
pi 3 - Is This a Raspberry Pi 3 B or B+? - Raspberry Pi Stack Exchange
Raspberry Pi 4 vs Raspberry Pi 3B+ — The MagPi magazine
How to Use Raspberry Pi 3 Model B+ V1.2 for the First Time! : 3 Steps - Instructables
Raspberry Pi 3 B+ Review and Performance Comparison
Raspberry Pi 4 Model B, 4GB DDR4 RAM Single Board Computer (RPI4-MODBP-4GB) for sale online
Raspberry Pi 5 vs. Raspberry Pi 4 Model B+: A Detailed Comparison, by Shreyas K
Setting up a Raspberry Pi 3 as an Access Point - SparkFun Learn