Quality of Sounder on Garmin 550c versus 551s

Hi lads,

I'm looking at a new unit and I've read a few posts on here about the above 2 units.

I'm thinking about going for the all in one option of the Garmin 551s but was wondering if there is much of a difference between the sounder on the 551s and the 550c?
From what I've seen/read on youtube/forums etc, the 550c seems to have a lot more colour differentiation for different types of bottom etc. Is that really the case? or do they both perform equally?

Thanks
Colm