osx 10.3+sme 6 (not gone to 6.0.1 yet) - so far no problems at all.
there are no "pure" os9 systems anywhere left - I did switch and do not regret. 

 the users always say that it "must"be faster and whatnot ....
though it is not main fileserver - just testing sme at the moment to switch the outgrown quantum (now defunt/merged) "snap server" - nas box with a www interface "quite like" sme. (and linux inside too - or so I think)
the usual thing about the 32 char filenames - and thus filetransfers OSX->sme may fail due to the fact that some files named inapropriately (also any symbols above 128 may make copy fail 

 ) 
one more thing _ I do try to setup the atalk connections using ip address not the atalk name - thus the speeds are better (no switching phase pure atalk/ip_atalk and so on) 
also if that's osx10.3+ then smb://servername is a good choice to connect - the only drawback is that it does not hide the unnecesary/afp files.
tested the gigabit net though the "real life™" tests make me feel the numbers should be lower. (this is over network using atalk)
QuickBench™ 2.1 Test Results File
©2003 Intech Software Corp.
Test file created on Wednesday, April 21, 2004 at 7:32:04 PM
Test Volume name: Home directory
Xfer Size     Sequential Read   Sequential Write    Random Read      Random Write
1 KByte      3.923 MB/sec      429.000 KB/sec    4.822 MB/sec      362.000 KB/sec
2 KBytes     7.342 MB/sec      941.000 KB/sec    7.958 MB/sec      688.000 KB/sec
4 KBytes     5.189 MB/sec      1.957 MB/sec      10.672 MB/sec     1.442 MB/sec
8 KBytes     382.000 KB/sec    1.856 MB/sec      251.000 KB/sec    925.000 KB/sec
16 KBytes    805.000 KB/sec    3.090 MB/sec      811.000 KB/sec    270.000 KB/sec
32 KBytes    17.152 MB/sec     2.973 MB/sec      21.200 MB/sec     7.601 MB/sec
64 KBytes    34.581 MB/sec     10.632 MB/sec     34.812 MB/sec     8.737 MB/sec
128 KBytes   25.463 MB/sec     11.854 MB/sec     26.333 MB/sec     13.000 MB/sec
256 KBytes   39.856 MB/sec     17.017 MB/sec     39.759 MB/sec     11.564 MB/sec
512 KBytes   32.479 MB/sec     19.062 MB/sec     33.250 MB/sec     17.026 MB/sec
1024 KBytes  39.055 MB/sec     18.982 MB/sec     40.865 MB/sec     5.370 MB/sec
Extended Test Size: 20 MB    Read: 16.449 MB/sec        Write: 23.564 MB/sec    
Extended Test Size: 30 MB    Read: 35.903 MB/sec        Write: 9.307 MB/sec     
Extended Test Size: 40 MB    Read: 25.327 MB/sec        Write: 22.944 MB/sec    
Extended Test Size: 50 MB    Read: 29.089 MB/sec        Write: 17.819 MB/sec    
Extended Test Size: 60 MB    Read: 23.636 MB/sec        Write: 17.051 MB/sec    
Extended Test Size: 70 MB    Read: 29.892 MB/sec        Write: 10.691 MB/sec    
Extended Test Size: 80 MB    Read: 32.199 MB/sec        Write: 19.491 MB/sec    
Extended Test Size: 90 MB    Read: 32.448 MB/sec        Write: 11.517 MB/sec    
Extended Test Size: 100 MB    Read: 30.154 MB/sec        Write: 10.739 MB/sec