Some comment on the posting subject: I doubt that the hrm-belt to watch transfer protocol has an effect on the accuracy, unless the signal is disrupted.
If there are problems, it should be the belt itself or possibly the device processing the hrm-data that is the problem, but I cannot say.
ANT+ has a lot of other possibilities, matching different type of sensors. For instance, I doubt that a Footpod or Power sensor from Globalsat makes sense, but there are suppliers. Good to hear that the main plan is to use ANT+.
I am curious about "lunch run" scenario, whar is this? 
We use the same scenario on distance calculation, but it still has slight different. I would like to know where did you check distacne, from SportTracks or on device? There are little different results.
I have kind of a deal with flexible worktime: I take longer lunches and stay longer in the evenings when needed.
Especially at this time of year, I only get some sun when going to work, but it is dark when I go home, so it is nice to get some sun.
Still, I cannot wait too long time for GPS fixes, I have colleagues waiting for me. Even if the GH-625XT locks fast, the handling if starting the timer before GPS fix is a bug to me: That data is seem to just be deleted. Well, that is a separate topic.
Sure the distance calculations differ between the device (lap markers can be used after activities), Globalsat speed track converted to distance track, and point to point (what SportTracks uses). They all differ, but point in the same direction. (Garmin has a separate distance track, so there device track can be studied in detail, which is useful when comparing like this, but not much in normal use.) I have sent some summaries, you can get the complete data.
ST Trails plugin has an update on Google Code with some instructions:http://code.google.com/p/trails/wiki/Tutorials#Compare_Data_Sources
The Globalsat speed track to distance importer for ST import plugin is not officially released. I have too many open questions about the com protocol still (I have sent emails...). I guess some will be resolved when TGP is updated.