mind you, numbers are just numbers for marketing purpose... maybe the 43 is in fact a 44 and the 47... a 46... both will sit in betwen the 35 and the 70 !
in my opinion, a 55 is much closer to a 70, than a 45 to a 35 !
i have 35,45,55,90,120M,180... the 45 was the final addition to the kit... at the end, i'm using it the most !