Again under the worst case scenario, with a poorly ventilated case, full CPU and GPU load, sequential writes throttled from 1600MB/sec to 400MB/sec after 21 seconds. So after copying 33.6GB.
But that worst case scenario is bullshit. You’re only at full GPU load while benchmarking or high-end gaming. CUDA use rendering video or whatever won’t get there. So yeah, if you’re playing The Witcher 3 and simultaneously copying over 30GB of data from one NVMe SSD to another in a poorly ventilated case, your SSD will throttle down to “only” 400MB/sec.
The heatsink is simply not necessary.