My RX480 runs Doom at 125FPS on my 2560x1440 monitor with pretty decent settings....Lots of games run well in excess of 100FPS even on High settings. Of course, if 75FPS is acceptable to you, might as well save the power/heat/noise.
VG245H = 40-75Hz VRR on HDMI. Did you make sure to enable FreeSync on the monitor menus and AMD settings?
Red Devil? As-in the triple fan cooler?
We should have you monitor your GPU frequency, voltage, and temp during load. Can you fire up FurMark and GPUz and report your results?
Just to be clear about "Chill". It's a power saving feature offers up two FPS numbers to the user (must adjust this on a per-game basis).
- The higher number tells the card a target max framerate. If the card is able to generate framerates in excess of this setting while at max frequency, the GPU will automatically down-clock itself so that it's not generating more frames than you need, which saves power. As King_V said, set this to your monitor's 75Hz/FPS limit.
- The lower number allows the GPU to reduce its frequency even further during "scenes with little/no on-screen movement" (aka take your hands off the keyboard/mouse and watch the butterflies). For you, I'd recommend setting this at 45FPS so you can limit the instances where you might accidentally dip below your monitor's 40Hz/FPS limit (the split second where you begin moving again).
I'd recommend adjusting your in-game settings to target ~60-75FPS
BEFORE you enable Chill.