X & M prop series

[Stingray]

Hi,
Can someone explain what are the differences between M & X series on Octura prop (X645 & M645 for example)? :help:
Which one is best ? What are the advantages/disadvantages of each of them ? :confused1: Thanks !

[Fluid]

http://forums.offshoreelectrics.com/showthread.php?18258-Octura-quot-M-quot-series-props&highlight=props

http://forums.offshoreelectrics.com/showthread.php?21842-low-and-mid-lift-props&highlight=props

http://forums.offshoreelectrics.com/showthread.php?11779-Understanding-props&highlight=props

http://forums.offshoreelectrics.com/showthread.php?11497-is-there-much-difference-between-octura-y530-and-x430-props&highlight=props