I've tuned FT-1s in 4 different setups already. 5khz is garbage for any kind of SQ. You have a massive peak at 5khz to 8khz that EQ can never hope to make a dent in. In all 4 of the setups i had to high pass around 8khz to 10khz at -12 to -18 db slopes. The tweet still plays down to 4khz very loud and it naturally fixes the heavy nasty sibilant peak thats inherent in the FT-1s. I mean if you just want ear bleeding garbage sound thats loud and blaring, by all means go with the 5khz, just letting you know the inline crossover they include is already a 5khz low pass.
Assuming you have normal ears and enjoy quality, clean high output sound, you try to can lower the gain and cut the eq to hell to sound a bit more bearable but the inherent issue is still there and you cant really play that loud without the harshness coming back.
However with a proper crossover to tame it, the sound will not be harsh no matter how much power you try to put on it, your total overall clean output is much louder without sounding like sh*t at highest volumes. Overall sound is much more natural and detailed. Literally making them sound almost like silk domes while keeping the output.
09 sienna B pillar 6th order with 4 team ascendant 18s on two taramps 15ks
320 amp singer alt, 6 group 31 agms in the back (battery revamp in the works)
80 prs, 3 way front with head unit + amp crossovers, massive ct 2 german silk tweets, pwx 10s in the doors, PRVs 6mr500 ndy in the kick on ct 500.2 to the pwx 10s, ppi 900.4 bridged to prvs, ppi 600.2 to the tweeters.