I've had the same RAM in my machine for a while but just now started looking into how it runs and wonder how to best set it up in the BIOS. It's always been finnicky on both my MSI board and moreso on my Gigabyte board.
I've got two kits, 2x2GB RipjawX and a 2x4GB Kingston HyperX. This is the info from CPU-Z of both kits and what I'm currently at.

My Gigabyte 970A UD3 sets it at 1333MHz at 1.5V with factory defaults . If I set the XMP profile in the BIOS to 1600MHz it won't boot. If I set it to a setting called "Profile1", which I have no idea where it came from, and set clock speed manually to 1600MHz it boots. Doing this it still sets the voltage at 1.5v. This is what I've been running on for a while. Also if the timings are on auto in any setting, it won't boot but changing it to manual and leaving automatic settings there lets it boot. It makes no sense why it's so picky.
On my MSI board previously I ran on similar settings, and it also defaulted to 1333MHz but wasn't as picky if I set it to 1600MHz XMP.
What should I set it at? I'm wondering if my undervolting of the Kingston kit is causing my occasional stuttering or instability. I sometimes get crashes under heavy gaming load that freeze my entire system and make a buzzing sound through my speakers. Increasing voltage or decreasing CPU clocks don't seem to change it much, although I haven't tried full stock clocks yet.
Is there any harm to just set it at 1600MHz @ 1.65v and CAS 9?
I've got two kits, 2x2GB RipjawX and a 2x4GB Kingston HyperX. This is the info from CPU-Z of both kits and what I'm currently at.

My Gigabyte 970A UD3 sets it at 1333MHz at 1.5V with factory defaults . If I set the XMP profile in the BIOS to 1600MHz it won't boot. If I set it to a setting called "Profile1", which I have no idea where it came from, and set clock speed manually to 1600MHz it boots. Doing this it still sets the voltage at 1.5v. This is what I've been running on for a while. Also if the timings are on auto in any setting, it won't boot but changing it to manual and leaving automatic settings there lets it boot. It makes no sense why it's so picky.
On my MSI board previously I ran on similar settings, and it also defaulted to 1333MHz but wasn't as picky if I set it to 1600MHz XMP.
What should I set it at? I'm wondering if my undervolting of the Kingston kit is causing my occasional stuttering or instability. I sometimes get crashes under heavy gaming load that freeze my entire system and make a buzzing sound through my speakers. Increasing voltage or decreasing CPU clocks don't seem to change it much, although I haven't tried full stock clocks yet.
Is there any harm to just set it at 1600MHz @ 1.65v and CAS 9?