Maximum fence post centres/ arris rail length?

[Dave Jones]

2.4 between posts as arris tails come in 4.8 lengths. 
 

Pushing to 3m is lazy as they saving on a couple posts at the expense of quality.

[avabanana]

3 meter arris rails is the standard size and absolute fine. I am the director of a fencing company. We give a 5 year guarantee on our work and I've NEVER had a call back on an arris rail snapping at 3 meters in 10 years. You can't even buy 2.4 m arris rails in 99% of fencing suppliers and 4.8m I have never even heard of. 

[Onoff]

I've 300' of feather edge fencing running East/West across the valley. Concrete posts, 3 X 3m arris rails. Never had a problem. 

[Russdl]

Our fence was done with 3m arris rails for aesthetics. Any shorter and it seemed to me there would be too many post cluttering things up. I can’t fault the quality. (My nephew did it and he’s bigger than me.)