my $sftp = Net::SFTP::Foreign->new(host =>$host, user => $user, key_path => [$privkey, $pubkey] , more => '-v');

[... debug output ...]
Transferred: sent 32700048, received 60544 bytes, in 1.6 seconds
Bytes per second: sent 20997978.1, received 38877.7
[... more debug output ..]