It certainly could.

Buying a better GPU improves your graphics performance and that's basically unrelated to the area where a sandbox impacts performance.

Killing your web browser is probably just lowering memory pressure?

Sandboxes add overhead to syscalls. It's kind of similar to running under Wine, which also adds significant syscalls overhead. Wine also has a much more impactful DirectX translation layer, so your sandbox performance would be probably be much better than the Wine performance.