First off not to get too far off topic, any product is with is positives and it's compromises. I would agree that the Humminbird mapping does appear to be a bit slower from my observation. However, there are a number of forum complaints of Lowrance HDS GPS not exactly quick either. I spent about a year weighing differences and looked at this purchase as a total package.
As for the package, it seems a bit ridiculous that a person needs to spend $2000 on the HDS8 to get memory presets for your favorite views and two card slots, then add another $600 for a side scan module; assuming it stays on the market that long due to a patent infringement lawsuit. Garmin tends to be a faster GPS, but they are a GPS company that makes sonar units. The others are sonar companies with GPS capability. Weigh the pros and cons and pick your package. No one manufacturer is currently offering the ultimate solution in every category.
Back to the original post, you are fishing in Wisconsin as I am. I also debated the two mapping solutions. Lakemaster makes a compelling argument that their mapping is more accurate as they are scanning lakes providing the better of the inland lake contours. There are some neat features and they have good looking maps, but they just don't cover what I need to see. Many of the lakes that I fish are of no interest to Lakemaster at this time, but I can get map coverage with the Navionics. I would much rather have some idea of the water I am going over rather than only having 10% of my lakes covered with Lakemaster and then have to resort to paper maps. And for those larger lakes, both companies have spent time scanning those lakes to provide more accurate contours.
The suggestion is to make a list of lakes that you fish or intend to fish and then compare the map list by each mapping company. If you are into exploring many of the 15,000 lakes here, I am confident that for Wisconsin that the Navionics will win hands down in terms of number of maps available. When comparing the map card cost in terms of number of maps per dollar, again the Navionics will scream as a bargain.