I have two HDS5 units on the boat, trolling and transom. I'm looking at upgrading to a down scan and side scan. I'd like down on the front and down and side on the back. I saw the Garmin units in the store and they made me look twice. 73SV and 73DV. I've always had Lowrance and was thinking about the HDS7 but now I'm not sure after seeing Garmin. Any input would be great. Thank you.