Daeve, you're right - I've checked and the distance is about 99% accurate - which makes the speed discrepancies even stranger. I'm being told that my fastest pace in any given km is between 3-4 mins but my average is about 5mins+ (and the 3min/km pace was uphill!). Interestingly I also use the corrected elevation data, but it still comes out consistently lower than gmap, which is odd seeing as they use the same data set.
I don't think there is a recording mode setting on the 410 (or at least I haven't found it).
GPS isn't always that accurate. When I look at my speed plots, they are all over the place. I also usually get a few seconds stationary per km even when I haven't stopped. They can also underestiamte distance and elevation. I tend to look at avg pace /km and overall. Found this site the other day - useful for plotting routes gmap-pedometer.com