I would not regard the 350 magnet as being really small, 500gm ? as against the largest (pretty big) magnet 13"x8" with a 700gm? magnet. I put in question marks as this is from memory from many years ago. The 450 certainly has a small magnet, but the 150 had the smallest magnet of all the 13" x 8"s.
The EMI paper cone tweeter that sounded best to me were the early ones that had Alnico magnets.

