I've heard good things about the tower46, from what i understand its the same as the Vmax 46 we get here, i understand both are made by GM.

"I heard that the OS .46 LA does not last as long as the OS .46 FX. Is it true? and how long does it last?"

in short Nope, there are so many variables it is impossible to say without having them on the bench and tested to distruction, even then you may be testing an above ordinary LA against bottom of the barell FX or vice verce.

given good fuel, good treatment, correct proping, no contamination, etc etc both will last for many, many years, i have a second hand OS.20 that is probably 20 years old with 100's of hours running and it still purrs.