Bramble,
welcome aboard. The problems with overheating panniers are dependent on where the exhaust points, not what type it is. My standard can (with Y piece) torched the contents of my aluminium pannier, as the cut out for the exhaust didn't allow the exhaust gases to escape without hitting the pannier first.
It's important to remember that we are not talking about
radiant heat, but about where the 'jet efflux' goes. With variations in build tolerances, different Y pieces etc, the pipe can point in a variety of directions.
In my case I solved it by having a functional (= ugly

) extension welded to the end of the can to ensure the exhaust exited aft of the rear number plate (doesn't matter to me as the panniers are, at least for now, permanently fitted).
I've seen pictures of people with holes burnt through their system cases. I'd suggest that if you have any doubts, yoiu take the bike for a good thrash with the new can and panniers fitted and then feel the pannier just aft of where the exhaust gases exit immediately after you stop...
HTH
Mike
