[ICOM] 756PROIII_ROOFING_FILTER

[George]

Can anyone tell me of the advantage of a narrow roofing filter in a 
receiver?
I note that the ProIII is still sticking with a 15kc roofing filter and the 
Ten-Tec Orion has filters that are narrower and selectable at that.
I read the ARRL product review on the Orion and it did note that there was 
an advantage to narrow roofing filters to a degree. Their tests indicated 
that too narrow filters such as, 500 cycles isn't necessarily better.
Since Icom is sticking with a fixed 15kc roofing filter is it their opinion 
that a narrower filter isn't needed for adjacent strong signal operation.?
Also the very top end Yeasu 9000 also has selectable narrow roofing filters.
Is there any merit to the narrow roofing filter question?
If it were not needed why does the Orion offer selectable filters?
Thanks.
George