Nagg, might be a couple of silly questions/thoughts but..
Are you running the lastest software on the h'bird?
What sounder freq are you using on both units? are they both 200 or 200/83 etc...
I own both Lowrance and humminbird and think they are great units. I have an Elite 5 and 798cxi HD SI.
I am looking forward to seeing the comparison images, you have even got me thinking about doing some experiments myself.
Cheers,
Mike