First of all I'd like to say nice post.
Unfortunately... I don't think there's much of anything that can be done, really.
You've basically already tried everything, and your hardware is pretty ancient.
Here's a list of things you could try ontop of what you've already tried, just in case;
-Change the resolution in windows to the smallest, and use fullscreen in osu!
-Update your audio and GPU drivers
-Set your windows (and other stuff too, if applicable) power & performance options to always be at maximum performance.
-Use a 'light' skin (WITHOUT @2x files)
-Set the osu!.exe process priority to 'high' in the task manager
Unfortunately... I don't think there's much of anything that can be done, really.
You've basically already tried everything, and your hardware is pretty ancient.
Here's a list of things you could try ontop of what you've already tried, just in case;
-Change the resolution in windows to the smallest, and use fullscreen in osu!
-Update your audio and GPU drivers
-Set your windows (and other stuff too, if applicable) power & performance options to always be at maximum performance.
-Use a 'light' skin (WITHOUT @2x files)
-Set the osu!.exe process priority to 'high' in the task manager