Disabled 'Shake mouse pointer to locate' setting in El Capitan but still get big cursor
That just sounds like a bug to me. Really, like with all beta software, bugs are to be encountered in the OS X El Capitan Public Beta. In fact, that's the point of betas, let certain users find and report bugs so that Apple, or whatever developer, can fix them before the software reaches mainstream adoption. So, unfortunately, all you can really do is report that bug to Apple, using Feedback Assistant. If you really hate it, then you could either wait for the public release of El Capitan in a couple of weeks or downgrade to Yosemite. You could also try installing El Capitan again, but it just like a bug in the beta software to me.