GPS Elevation is rubbish, it jitters just as much as speed, I've used ones with and without barometers side by side and and the baro is nice and smooth, not a jumble of steps.
It does use the GPS to help it calibrate by averaging out (which is safe, and also the way it does the automatic wheel size, which is best to measure still). A good comparison (if one suddenly changes/spikes.. it's wrong) would help spikes, but this is too clever for Garmin.
Half of these problems occur on the 305 too, Garmin don't give a toss.
Try this... delete part of your lap and the file will still output the whole track... it will put the deleted part of the track into the left over lap section, it's stupid. Apparently you shouldn't delete the lap on the unit if you plan to use it on the machine (although the unit still uses the TOTAL time of all the laps).
Calorific calculations are rubbish anyway.
Another issue I have, is it will display your wheel speed, but won't record it if GPS fix is present, i'd rather the wheel speed be stored (or both).
Pauses are removed in the "total moving time" calculation.
I can show the numeric bearing on my 305 :/
Next unit, i'm not bothering with Garmin, their old products were ace, but their name doesn't really apply to these "consumer" units.