Are the beds already there or are you making the circles for the first time?
Is a bed edger only going to outline the circle's edge, like it is called an edger. I know some one does make a bed edger that has a longer horizontal blade for cutting turf back a little farther but, if more turf closer to tree than it would take alot of time to keep going around to make a 3' circle.
I would think a actual turf cutter would do better if there is no exsisting bed. I use a Quail kick type sod cutter and edger for this type work, so I never have needed or used a actual edger, but 165 trees would wear you out kicking, for sure.
I had a mailer sent to me a while back showing a tree circle cut and mulched in 5 minutes. I think it was a small steerable sod cutter, heck maybe it was a bed edger. Anyway, I think it was from Turfco. Not sure if they have a web site.