Are My PC Upgrades Worth It or Should I Switch to a New Platform?

I believe you should just install the 5090 into your existing build. After that, if you experience any issues, you can think about more extensive upgrades down the line. Also, I've had a great experience with the cooling setup you already have, so unless something's amiss, that shouldn’t be a problem.

Honestly, if you're contemplating switching platforms, the AM5 9800X3D would be a strong contender due to its compatibility and performance. Many people find Ryzen a better overall option these days, but I understand you're sticking with Intel for specific reasons.

If I were you, I'd prioritize the motherboard upgrade first. The i9 is a solid choice, but since you're using a 5090, you might also consider moving to a Ryzen 9 9950X3D setup for an even better balance between productivity and gaming. The cost of RAM is a bit high right now, but you’ve got 64GB already, so just swapping the CPU and motherboard should enhance your performance significantly.

Honestly, upgrading from the 13700K to the i9 14900K or going Ultra 9 isn't going to make a huge difference in gaming performance, especially if you're playing at higher resolutions with that 5090. I'd suggest focusing on getting a better cooler and perhaps a new case to improve airflow first. Plus, just a heads-up: those Gigabyte 50 series cards have had some thermal issues, especially if you're mounting vertically in the Hyte Y70.

I’d keep it simple and just swap the 4090 for the 5090 in your current setup before diving into major upgrades. See how your system performs; if you’re happy with it, then you don’t need to change much else. If you run into any performance bottlenecks, then you can always consider moving to an AM5 setup later.