Hmm. If the hostname lookup / ident response are cached ioftpd should be instant. If the ident request is not being replied to because a router/firewall is stealthing the port (as opposed to returning connection failed) the servers might be using different timeouts because if they got the response they would have the same performance I believe.
There is one optimization I just thought of that might make a difference. It's possible that if the login account doesn't require an ident (i.e. hostmask is *@...) glftpd/drftpd might just allow the login immediately. This means that they couldn't know if they would ever get a response at this point so the login log entry wouldn't be complete, but perhaps they add a new one if they eventually get a response or something. For a public server where lots of users might not have the identd port forwarded or something that might make a lot of sense... I'll take a look at options there.
I guess I never notice this delay since I respond to identd requests locally
Check out (ioFTPD.ini):
Ident_Timeout = 5 # Set ident timeout (10)
Hostname_Cache_Duration = 1800 # Seconds cached hostname is valid
Ident_Cache_Duration = 120 # Seconds cached ident is valid (1800)
If you do NOT have logins that require an ident response (i.e. no xyz@...) you can set Ident_Timeout to 1 or 2 or something which should solve your problem. If you do have hostmasks with idents in them this is probably a bad thing because a little hickup and people won't be able to login and they won't know why.