Not really AIBU (sorry!) but I guess I know very few people with five years between their children (though my friend assures me "farmers always seem to have five year age gaps and I always think they're very sensible" 
)
Both DH and I were 3 years with our siblings - I have to say I didn't always get on with my sister and it did get quite bad at times which I think has had lasting effects for both of us. DH gets on with his now but not when younger and apparently decided to apologise to his younger brother when he was around 20 for how he'd treated him. Another friend with a brother five years older completely idolised him, which sounds lovely!
So in some ways I can see less competition between a bigger ages gap; at the same time there are loads of shared memories which are fabulous because we were closeish in age. So joint family things may be tricky, watching films etc.
I guess I'm just looking for experiences/ perceptions. Not a lot we can physically do about it!