I run a massive production studio and just recently did a track with the Hawked Poly800mk2 playing the main riff and I heard no lag (and I'm pretty anal about these kinds of things). Maybe this is more pronounced on Poly800mk1/EX-800 due to different hardware?
Here's the track with the Poly800mk2 BTW if anyone's curious:
http://soundcloud.com/siraltus/rob-hubbard-jet-set-willy-serge-p-remix--Serge