I like to get 14 radius or more. The less the bots dance around snatching piles the better and soaking up all those health globes while in combat will let your bot ignore aoe (i have the avoidance for most everything set off and down at 20% for the explosion crap).
You can set them to ignore smaller piles of gold and they'll still soak up almost everything while keeping the run smooth. I'm not finding much that sells on the ah for more than 20mil so picking up gold is pretty important to me. The monk has been pulling in 600gph and likely more with some adjustments I've made today.
I gave in and got the innas 4 piece (dropped depth diggers and rare belt and replaced lacuni's to avoid wasted movement stats) and dropped serenity for wave of light. Modified his route as well so we'll see how it goes
(Btw my monk is a far superior farmer to the two barbs. I'm considering selling them at para 100 and getting 2 more monks).