I doubt it's as noticeable as you make it out to be. I use the default kernel shipped with OpenSUSE Tumbleweed and the system is acceptably responsive while under load, with the main exception being low memory situations (i.e. heavy swap usage). But I expect the Zen scheduler to have similar issues.

Then again, I probably have more tolerance for poor responsiveness because I rarely run my system to its limits (unless compiling) and rarely interact with other apps while playing games.