Why hitches are a streaming problem
Big maps don't fit in VRAM and RAM all at once, so the engine constantly pulls textures, meshes and audio off the drive as you move. If the drive responds slowly or chokes on lots of small requests, the frame is ready but its data isn't — and the game stalls for a fraction of a second. On an HDD this is worse because of seek time: random reads of many small files are several times slower than on an SSD.
Telling the drive apart from the GPU
Run an overlay (MSI Afterburner, an in-game monitor, or Task Manager) and watch disk activity at the moment of a hitch. If the drive spikes toward 100% right as you stall while the GPU sits underutilized, it points to a loading problem rather than a rendering one. Note that Task Manager's 100% means the drive's active time, not its actual throughput, so treat it as a hint rather than proof. Hitches on your first run through a new zone that vanish on the second pass are a textbook sign of disk streaming.
What actually helps
Moving the game itself onto an SSD — not just Windows — removes most of these hitches, especially in titles like Rust that are full of small assets. The big jump is going from an HDD to an SSD; for loading hitches specifically, the gap between a SATA SSD and an NVMe drive is much smaller, so you don't need to chase NVMe for this. Keep some free space: a nearly full SSD loses write speed, which hurts shader caching and downloads. Enough RAM matters too — when memory runs short, Windows leans harder on the page file on disk, reintroducing the same stutters.
Verdict
An SSD won't raise your average FPS, but it removes exactly the choppy loading hitches that ruin the feel of a game the most. Confirm with monitoring that the stutters come from the drive first, then spend — a storage upgrade often buys more smoothness here than a new GPU does.