I am in the process of looking for a color graph to replace my old one. I bought a "02" 19 ft. Starcraft (another story) this summer with a Lowrance X-98 D/F on it. The graph is OK but I would like to upgrade to a color unit that that I can use with a downrigger. I want to stay with Lowrance if I can. I use a stand alone GPS and haven't had any problems but was wondering if it would be better if I had them both in one unit? I will be fishing in fresh water mostly for walleye & salmon. I have been sort of leaning towards the 510C but also have been looking at the LMS 500 series to. Any input would be appreciated. Thanks