pssh -H h1 -H h2 -P "tail -n 1000 /var/log/x.log"
You'll want -i to avoid the buffered output that would make the log output hard to read.
And if your command doesn't contain anything that you need to escape from the shell, you don't need to quote the command.
And finally, since it implements BSD-style short flags correctly, so you can do "-Pi" instead of "-P -i".
Handy with a pre-defined list of hosts, too:
pssh -Pi -H "hosts.txt" tail -f /var/log/haproxy.log
pssh -Pi -H `cat hosts.txt | grep prod` tail -f /var/log/haproxy.log