mustardoverlordthis might be kind of a dumb question but I've only ever used a TN panel, how noticeable is that loss in response time in actual competitive games? anyone have experience with it or any newer IPS being advertised with a 1ms response time?
You will not be able to perceive the lower response time just based on feel (unless you're coming from a monitor with a high response time). You want a low response time on your monitor because it minimizes image ghosting which will help with clarity and image quality. Ghosting will make it look like you have motion blur on.
This of course highly depends on the monitor because some manufactures make their monitors have 1ms but have horrible ghosting. The LG 27GL850 is a really good monitor and doesn't have that issue. Though the "below 5ms" is pure marketing because it achieves it by introducing other artifacts like ghosting. As long as you keep the setting of the response time to just "Fast" and not "Faster" it will be fine.
Faster
https://i.imgur.com/GSv3czO.png
Fast