The Payback 720p |WORK|
I would try to OC the RAM and the GPU Core. You could also try if you have the option to create a custom resolution that is lower than 720p but still retains 16:9 ratio so it would not look stretched. If Chrome opens by itself then I do suggest to do a clean Windows Install. You can also try a tool called CRU that can do this if you cant find the option in the Radeon Settings. I will reply back if you need more help.
The Payback 720p
The custom resolution setting you found in the radeon panel is used to build up a custom resolution that your panel would not support natively.It have nothing to do with the ingame resolution, the one that matter. The only thing you can do is overclock a bit the cpu/gpu if you have decent cooling system, get the game at 720p low details everywhere.You could also edit the config file of the game to tune even further the game detail settings. You can maybe disable more details that the game setting allow you, increasing a bit the performances.