I've been solo swarming here since I think 48 (where it was more than a level per pull) to 55 where it's slowed to about 4 blue a pull.
I find the safest spot is near -2000,1000 (
http://wiki.project1999.org/Burning_Wood) right at the foot of that crater there's a fallen tree, I make circles just west of that fallen tree with the tree tangential to the east side of my circle (there's nice visual cues of where you are when watching from above because you have the grass/burn interface before you run into the fallen tree, etc). At worst you'll get a bee pathing through which is fine as long as you pull it first... it may respawn while you kill the high hp mobs but by that time you'll have a corpse outline of your circle so you can be fully aware of where you are running and it won't matter. I don't like SF zone much, maybe it's good but I always felt hastled by the nastier roamers there (casting sarnaks etc) and it's a bit out of the way of good mobs.