Bought this kingston xs2000 a while ago. It's officially rated for "up to" 2000Mb\s read\write but slows to a crawl after 30GB have been copied. Fyi, I'm copying files from an internal nvme (samsung 980 pro) via a usb 3.0 cable, so this kingston ssd is the only bottleneck.
Check reviews that test writes over ~15 minutes. This kingston holds out the longest but then has a very low floor https://cdn.mos.cms.futurecdn.net/cqJ6pXctEd5BKJVLJN7TCD-1200-80.png
It's a worst case senario for all drives though, and they will drop in throughtput. Caches run out, heat build up, power supply gets strained, it's rough.