[zaphod24]

Welcome back! Nice to see you moved from WMC to MythTV. I also use MythTV with an HD Homerun Prime. I found the following settings in advancesettings.xml helped make sure the cache was filled a bit more when playing live TV:

<pvr>
<minvideocachelevel>25</minvideocachelevel>
<minaudiocachelevel>25</minaudiocachelevel>
<cacheindvdplayer>true</cacheindvdplayer>
</pvr>

I also use the following overclocking settings which work quite well playing back 1080i60:

dtoverlay=sdhost,overclock_50=84
gpu_mem_1024=320
arm_freq=1050
core_freq=525
gpu_freq=350
over_voltage=4

With the latest firmware, turbo mode is started automatically during playback and the PI goes back to normal when playback ends.