[popcornmix]

What is the purpose of avoid_pwm_pll?

See: http://elinux.org/RPiconfig

Don't dedicate a pll to PWM audio. This will reduce analogue audio quality slightly. The spare PLL allows the core_freq to be set independently from the rest of the gpu allowing more control over overclocking. Default 0

I wouldn't bother. Set arm_freq, core_freq and sdram_freq as high as you can.
There's no point overclocking isp_freq, h264_freq, v3d_freq as they are never a bottleneck running kodi.