Why is my new PC with a 5070 and i5 14600k underperforming?

Your 3DMark score seems okay, just a bit below average. I think you're on the right track with addressing RAM issues. For best performance, consider using matched pairs of RAM sticks that are tested for compatibility.

Having three RAM modules can slow things down a bit, especially if they're not matched well. It's crucial to check the speed of your RAM and confirm if XMP is enabled in your BIOS. Make sure your RAM is set up in dual-channel configuration too. What's the speed of your RAM? If it's running at 2133MHz or slower, you might be losing out on performance.

Don't stress too much; bad 3DMark results usually point to a fixable issue rather than a hardware fault. First, ensure your GPU is in PCIe x16 mode; you can check that using GPU-Z while under load. Additionally, enabling Resizable BAR could boost your performance by 5 to 15%. Lastly, what PSU do you have? An underpowered unit can throttle performance.

It sounds like your CPU clock speeds might be lower than they should be. There could be CPU throttling happening—often from high temperatures or inadequate power delivery from the motherboard, which can bottleneck your GPU. I'd recommend installing HWINFO to monitor CPU temperature and power usage while gaming. Also, what kind of CPU cooler are you using?

I noticed you're using two 8GB sticks alongside a 16GB stick. Mismatched RAM can cause unique performance issues. When you have time, try running the benchmark with just one of the 8GB sticks or just the 16GB stick alone to see if that helps.