I need some education please. I mainly fish Lake Cumberland and the Ohio River. I'm getting ready to order a new Lowrance and don't know if I should go with the single 200 khz or dual 50/200 khz transducer. I had the single on my last unit and it worked fine but have the chance to get the dual for the same price this go around. What are your thoughts to the advantages/disadvantages of the dual freq transducer?