You could try running the ssh server deamon in debug mode with -d. This stops it from backgrounding itself, quits after one connection session and outputs verbose debug information to syslog. That should provide details on which ciphers get selected etc.
As for performance, as far as I know, for short connections, most time is spent generating and exchanging session keys and negotiating client/server settings. Have you considered comparing sftp to ftp? At least you can guarantee that there will be no encryption overhead with ftp.
I did a quick search: Apparently, blowfish is about 11 times faster than 3DES but no-one can show test resuts to prove it makes ANY difference over a network! There may not be any differences to measure (under Linux).
For a definitive answer, I suggest the OpenSSH mailing lists: http://www.openssh.org/list.html