I’ve been using SportsTracker on an N95 for a while. Flatteringly, it reckons my morning off road ride on a singlespeed is at an average of over 20Mph, and is 17 miles long. It’s neither, I can assure you! Running is also problematic – I thought I’d get a better track off the GPS moving slower, but no go. This is in an area of good coverage, so AGPS should help out.
The N79 is a newer phone, so it may have a more accurate GPS unit / better software. I was thinking of getting the N79 Active if it ever launched in this country (it may do tomorrow – mobile phone companies love quarterly launches) but bear in mind you may have to get locked in to a longish contract to qualify for this phone FOC.