Hey mate,
have you checked out the eagle Seafinder 480 DF,
dual freq, 500RMS, and 480X480 pixels, 5" screen, the same features as lowrance but with better clarity and cheaper.
Furuno LS 4100 is less powerful and has less pixels so I don't believe is in the same league.
Bias has the eagle at the moment for $469.00.
A good deal if you ask me.
The number of pixels do count for a lot, Just thought I would put my 2 bobs worth in.
Ps I don't work for eagle or Bias.