What's the capacity of your 830? If it's 128GB then it's behaving normally, if it's 256-512GB then it's a bit bellow the 330MB/s nominal speed.
If it's the 128GB then the speed isn't problematic, since it's rated for up to 320MB/s.yes, it's the 128GB drive. I was thinking it used to be around 400MB/s, but that was awhile back, and I could be mistaken