If long haul then no, I don't rush to board if I'm already flying in J. However, be careful if you fly PEY, those overhead gets filled up by people can't find space in Y and the cabin crew just put them in PEY overhead instead, regardless if PEY people have boarded or not. I've seem PEY that boarded late with no space overhead (of course the last recourse is put them in empty J overheads by the cabin crew)