My Latency Is Great In The Browser But Spikes Badly In One Game

Your measurement is doing its job: it has cleanly eliminated the controller, the cable and the operating system's input path. A consistent 10 to 12ms with a tight spread across sessions is as good as a wired pad gets, so whatever is happening is downstream of input entirely.

Intermittent spikes on a rough twenty to thirty second cycle, in one game only, have a short list of likely causes. Shader compilation is the most common on modern PC titles: the engine hits a new effect, compiles a shader, and stalls for a fraction of a second. It clusters early in a session and reduces as the cache fills, so if it improves the longer you play, that is your answer. Asset streaming is next, where the engine pauses to load, and it correlates with movement through the world rather than with a clock. Third is something outside the game on a timer: a background scan, a cloud sync, a telemetry upload or a launcher doing housekeeping. Those are the ones that genuinely do land on a regular interval, which fits your description most closely.

On measuring it, which is the better half of your question. Do not chase this by feel. Turn on the game's own frame time graph if it has one, or use an overlay that logs frame times rather than average frame rate, because average frame rate hides exactly this. What you are looking for is a frame that takes tens of milliseconds while its neighbours take seven. Log a session and you will see the spikes as spikes, with timestamps, and then you can line them up against what you were doing and against what else was running.

Two high-yield things to try while you are at it: enable the game's shader pre-compilation option if it offers one, and watch resource usage during a spike. A storage device at 100% utilisation during each stall identifies streaming or a background scan immediately.