This is my battery of Grot Big Gunz Kannons from a recent game (hiding behind some cover).
In the new Ork Codex, these Big Gunz are now much better at hitting things.
Grotz in the new Codex now have a BS of 3 making their base to hit roll a 4+ which is one better than their bigger Ork cousins.
The only downside to the new Big Gunz rules is that Zzap Guns no longer automatically hit (according to the letter of the rules) and as they cost more points and have an average strength lower than Kannons, are not longer a real option anymore.
I am hoping the imminent Ork Codex FAQ will clarify the Zzap Gun rules.