I've just replaced an Acer Predator 27" IPS which failed after 9 years sterling service with a 27" LG OLED 27GS95QE-B which cost £600.
The major differences are:
Text was clearer on the IPS - there is fringing on the OLED, but this can be minimised somewhat using different cleartext settings.
The LG seems slightly smaller, even though both monitors are called 27"
The LG seems way smoother, much faster response time. Variable refresh rate works great.
The OLED colours and contrast completely blow the Acer's IPS panel away. HDR looks incredible in games. Even without HDR watching TV and movies on the monitor is much nicer.
You have to deal with the OLED's maintenance modes that help reduce burn-in. No such issues on an IPS.
Note that many OLEDs have glossy screens, which improve contrast but are awful for reflections. I chose the LG because it had a matt screen.