There will be no monitor with HDMI 2.1, and to understand more I've made this thread previously, I hope it helps:
I hope this helps! And a high-end, considered as the best TV for gaming to some, the LG CX (although it's 40Gbps not 48Gbps compared to previous C9) 4K is 4x times 1080p quality, if you're still watching 4K content on a 1080p screen then you're only recieving a maximum of 25% of the...
www.neogaf.com
I you want OLED go for LG C9 and CX, but you'll need to deal with weak motion control at 24-30fps and potential burn-in and banding concerns.
If you want LCD LED go for Sony X900H, best motion, upscaling, color processing at a budget price. But you need to live with slight blooming that LCD's have with local dimming methods (can be turned off and have less darker blacks) and no perfect blacks in dark rooms. I'm personally going for this one 65-85".
In terms of input lag HDMI 2.1 are toe-to-toe with monitors at 1080p/1440p with extra 4K and 120Hz, VRR, ALLM.
Only problem is if you think 48-55" is too big.