Cat & stubby vs y piece and remus

[The Phantom Pieman]

For those who have done this mod, what are the advantages ...

I have a remus / y piece
Taking off the cat on mine seems to have given mid range, more drivability. But the Remus heats up the pannier a tad too much

I now have a stubby that could go directly on the cat ( but that weighs about 500kgs) - and it would sort the pannier issues

What are the pros/cons?

Thanks