Will DDR4 hold back an RX 9060 XT at 1440p?

I'd frame this as a 5600 versus 7500F decision, not just DDR4 versus DDR5. You're changing the CPU and platform along with the memory, so you can't pin the whole performance difference on the RAM.

The 7500F is the faster processor and gives you a newer platform with more room for future CPU upgrades. If the extra $250 fits comfortably and you want to keep the system for a while, that's a reasonable reason to spend it.

For 1440p, the 5600 setup is a sensible way to save money. In games where the GPU is doing most of the limiting, the CPU and memory difference may not make a big difference to frame rates. CPU-heavy games and situations are another story, so there isn't one percentage that applies everywhere.

I'd also price out what that $250 saving does for the graphics card. At 1440p, putting more of the budget toward a stronger GPU could make a bigger difference than moving from the 5600 platform to the 7500F. Compare complete build prices and GPU benchmarks before deciding, though.

Don't take either extreme about RAM speed as a rule. Memory can affect gaming performance, especially when you're CPU-limited, but DDR4 doesn't automatically cripple a build. Look for benchmarks of both processors with a similar GPU, resolution, and games or settings to the ones you care about.

For unreleased games, there's no reliable way to know the performance difference yet.