[1000mp] RTTY filtering

[Edward W Badger]

I am new to RTTY  (and thoroughly enjoying the mode) so excuse a facile question....
I use MMTTY software, and AFSK  running from my PC sound card, buttons on FT1000MP MKV field set to "PKT & LSB" 
I use a Rigblaster plus interface.
It works absolutely fine no problems, I use both NOR & NAR2 (which I presume is the 500Hz filter) on the bandwidth settings, I have read that the receiver would benefit greatly selectivity wise by using a 250Hz filter?
Which one do I fit is it the 2nd IF one YF-114CN...or the 3rd IF one YF-110CN.. or do I have fit them both (hope not because of cost!).
Presumably the 500Hz filter becomes "redundant"  only to be reset by the menu selection 5-4? and "losing "the 250Hz one.
Would the "new" 250Hz filter (wherever fitted) also be useable on the CW setting?
Any answers much appreciated 
73 Ted 
G3OZN