How much does 32GB of RAM help for 1440p gaming on an RTX 4070?

Not much — maybe 0-5% in most games, and zero in many. 16GB is still plenty for 1440p gaming because the RTX 4070 is usually GPU-bound at that resolution. The few exceptions are games like Hogwarts Legacy or heavily modded titles, but even then the gain is small. If you already have 16GB, upgrading is a waste of money unless you’re modding or streaming.