Wow, that test at the top of the first image is a crazy outlier compared to the rest of the results at your house. I'd be interested to know what else was different about that test other than time of day.
As far as my experience, after 1.5 days of usage (and many comparative speed tests), the data signal on the S3 appears to be somewhere between the Nexus (which I had for 1 week before trading it in due to its horrible signal) and Rezound (which I still have as my backup). The S3 speed tests have been, on average, about 60% of what I was getting on the Rezound in the same places, but still "good enough." It also appears to bounce between 3G and 4G a lot more in fringe areas (i.e. my house and office) - the weird thing is that this usually happens only when I'm holding/handling the device. When I set it down, it holds 4G signal much more consistently. I wonder if antenna design is causing this behavior somehow... I'll play with it some more and see if I can pin down some definitive patterns.
So far it has passed test #1: maintaining steady 4G signal at the office (while sitting on the desk) to allow me to listen to streaming media. Tomorrow will be the next test: I have 5 hours of conference calls from home, and I'll be counting the dropped calls and taking note of the quality.