I had seen some benchmarks several years ago around the time when the significant GC optimizations had been made, and I could've sworn they were on the order of single-digit microseconds; however, I can't find any of those benchmarks today and indeed any benchmarks are hard to come by except for some pathological cases with enormous heaps. Maybe that single-digit  µs values was a misremembering on my part. Even if it's sub-millisecond that's plenty for a high 60Hz video game.