[wrxtasy]

I bought a new TV 4k (Sony Bravia KD-65XE9005). When I set resolution for 4k in Kodi on my Odroid C2 I get a small stutter, 1080 is working good. Why is that?

1) Make sure you are actually connected to a HDMI 2.0 port on your 4K TV. HDMI 1.4 is limited to 2160p@30Hz = 4K@30fps

2) No need to run a 4K Kodi user interface resolution because if you enable Kodi refresh switching in settings, 1080p > 4K resolution switching will happen automatically when you watch 4K content.
You also want your 4K TV using it's superior 1080p > 4K picture upscaling hardware giving you higher quality picture outputs. 1080p is what you will be viewing most of the time anyway.

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This should give you what you want:

LibreELEC-Odroid_C2.aarch64-8.2.2-NR-LFE-SUSPEND.img.gz

And does this also allow oc to 1,7GHz?

Yes so long as you use a decent power supply. Change to 1.752GHz by modifying the boot.ini file on the SD/eMMC card.