Unfortunately you're comparing apples with oranges. 450Mb/s = 56MB/s which is about on par with what you're seeing in real life. They're both giving you the same reading (but one is in bits, one is in bytes). You need to divide 450 by 8 to get the same measure for both. (In your question, you've got the capitalisation the other way around, now I can only hope/assume that this is a typo error, because if you reverse the capitalisation you get an almost perfect match)