slow ssh connections on LAN

[robertlaferla at comcast.net (Robert La Ferla)]

I have a LAN with two Gigabit switches (Linksys + Netgear) with at  
least CAT-5 cabling (maybe 5e but not CAT 6.)  Transfers using "scp"  
between two Linux hosts average 3.9MB/s.  All NICs are 100BT except  
for one Gigabit NIC so I should not expect Gigabit speeds but I do  
expect 100BT speeds.   I have also noticed that "ssh" logins usually  
take a long time (10-15 seconds).  What could be the problem?  How  
should I go about diagnosing it?  What tools should I use?  The LAN  
has a mix of Linux, Mac, Windows and VOIP systems.