relying on gps for elevation is problematic. there are devices that supplement this data will barometric readings. but relying on google maps to dictate where the road actually is is also problematic. for instance, that last turn before star hill is wider on google maps than it is in reality and at least in that section your gps is more acurate. to illustrate, just zoom in on google maps using the satelite view + "show labels" ~ you'll see the label is off a bit, and the turn is tighter than the overlay indicates.
so neither are perfect, but we probably don't need such resolution.
I'm still quite new to my 305, but for now, I go by the total elevation shown from the altimeter on the unit at the end of the ride. Unfortunately, it seems that it's tough to get that data back once you log another ride.