I've heard about this before but I'm still impressed about what a big difference it is.
I was formerly working for a same-race, Q 19 agent that I had 6.2 standing with, in .9 space.
I switch to an Amarr, Q -4 Agent, standing 0.0,
in .5 space and I'm usually getting at least five times the mission payouts as I did with the first agent.
If you're afraid of getting podded, I've found several .5 systems that have other .5 systems on either side - so as long as you're working kill missions, you won't be going into .4 or lower space. At least in my experience, level 1 agents never send you more than 1 jump away.
Extra bonus: Amarr agents seem to give out less ammo and more cold hard isk. Minmatar working for an Amarr
Edit: Oops, theres a .4 next door. Oh well, the payouts are worth it.