Er, 455mm is the length man not the width (if that's what you mean) so it wouldn't effect the hop compatibility. If you mean 'will the hop window be compatible' then yes, it is. It'll stick out the end by 15mm but like Monty says, but that's not a problem as the flash hider will conceal it.
6.01 will give you a negligible FPS increase, but a wider bore will give you better accuracy and allow a more consistent hop. If you're happy with the FPS of your stock one then go with the 6.03. Also, it'll be slightly less prone to jams.