When looking into fish finders what are the key things to look for. I was told that the higher the peak to peak watts the better. What else would one need to look at? The fishing I would use it for would be trolling for salmon and lake trout as well as bass. No salt water just fresh water fishing. Any help would be great. Also in looking into fish finders I noticed some indicate an RMS value, I am assuming this is some form of signal return?