A lot of guys use SI at the console and run DI at the bow on the trolling motor. I am currently switching to Humminbird's on the new boat and will be running SI at console and DI and 360 at the bow. I feel you can idle around with the big motor and find structure with the SI and set waypoints and then go to them and use the DI to get a better look at what is there. I had ran a HDS 5 at the console for several years and then added a HDS 7 and moved the 5 upfront. Huge difference in what you can see on the 2" larger unit and I never had the LSS1 hooked up before I sold it. I used it more for GPS mapping than anything. Go with the largest unit/screen within your budget. Do the HDS units you have now have Lake Insight mapping? That will make them worth more money when trying to sell. These units sell everyday on bassboatcentral.com classified's section. Great place to go see what they are currently bringing/worth.