CP-755Ti vs ND1424BT

Different sized voice coil, the 755Ti will go lower.
It would likely be my pick.

If i were you i would spend the 20-30€ difference and get a newer design ND3T with better performance, since you specified Ti.

LEAN has good prices on them.
 
I’ve got an opportunity to pick up either at a very good (and same) price second hand, so it’s between these two.

The 18S is only a 2.5” diagram so should go a bit higher than most 3” drivers, but obviously not as low as you point out.

But character would be interesting to hear.