From ssh2 to openssh

ssh-keygen -i -f id_dsa.pub > id_dsa_open.pub

From OpenSSH to ssh2

ssh-keygen -e -f id_dsa.pub > id_dsa_ssh2.pub

To increase speed on transfer you can force cipher to arcfour.
You can use same mechanism with rsync when you use ssh encapsulation.

scp -c arcfour <source> <destination>

rsync -av -e "ssh -c arcfour -l <username>" <Source> <Destination>

<span style="color:red">NOTE:</span> THis reduce your security though