What is the max number of sub folders any 1 directory can have before there's a major performance hit?

I have a directory on a NW6.5 sp5 server with 1,331 folders in it and it seems to be giving a couple of my newer machines fits. The older machines are having no issues. These machines are just acting like they're processing too much data in narrowing down where the folder is.

Its a shot in the dark I know, I just can't figure out why these two brand new machines are having issues accessing these specific directories. I've swapped out NIC's, data ports, switch ports, opened the directories from other machines.

The server drive has tons of space left so its not a space issue. Any thoughts?

Thanks in advance!