hey mark,
i have not used both, but have used a few others. the thing about your water your fishing is more important. fishing weeds with a wide angle transducer means more clutter or too much information from the weeds that is represented in a tiny space. so the idea would be to use the narrow beam so it shows less weeds in that same space. when your looking for those pockets that allow you to see deeper in the weeds, this is even more important.
i use the marcum lx9 and fish mainly 4 to 12 feet of water to bottom on one lake and has a max depth of 45 feet. and 15 to 27 feet on another. 27 feet is the deepest the later lake goes. i notice as it turns dark the fish move slowly back out to slightly deeper water. they are suspended fish some days and then they are foraging fish other days. i'd rather fish the edge of weed beds than trying to look thru them tho.
marcum digital units don't show the first 2.5 feet under the transducer. this is fine by me because my ice-55 would show tons of clutter instead in that same space. i would rather not have to watch that anyways. if a crappie is scouting and swims by you won't see it on sonar, but if it did see it it's gone anyway before you could react.
lowrance is more on the bottom of what most users use here.
here's a link to that fact.
http://www.iceshanty.com/ice_fishing/index.php?topic=331371.0another thing to consider is how well the sonar engine works. also, how to use it in the ice hole. marcum has you hold just the bottom of the transducer in it just so it gets wet. the air ruins how it functions. some thing else to consider is marcums new shuttle that is lithium and offers many advantages like being to night fish with it and have ram mounts on either side if you want them and usb power ports and 12 volt power port and a battery indicator and up to 40 hour run time. if you buy it in the package (with sonar attached) you'll save 100$ off of the 250$ price tag.
also, the marcum is designed for ice fishing firstly and can be fitted for open water, but is best used for ice while the lowrance it just the opposite. so things like the IR will be key here.