OLEDs are very quick, much quicker than IPS, so they are ideal for FPS.
The biggest thing you would notice right away is the way the colours really pop. The contrast is way better than the Predator. Not only that, but the colours are way better too - especially against an old IPS - red will have faded on your monitor now and side by side colours will look look tired and reds distinctly orange. You won't notice that until you pop the OLED next to it, but I guarantee you that you would be shocked.
Is it worth the money? Only you can say. It's a lot of money and there are downsides to OLED. Text fringing and burn-in being the main ones.