If we are talking about GPS signal, accuracy and ttif, that would be affected by whether A-GPS can be used at the location you are at, i.e. if there's GSM coverage (keep in mind it uses data, but only about 4-7KB per ttif). It could still pick a signal even without A-GPS but the chip is weaker and would require much longer time to get a fix (I've tried it with Nokia N95 8GB without A-GPS and sometimes takes over a minute, maybe more). With the A-GPS, I find it faster than any standalone BT receiver I've used, and keeps the lock as well as any.
As for navigation solutions etc., you should read the sticky in this forum " GPS and Mapping Guide for Beginners", which has some information on navigation software available for s60. I personally like Nokia's maps, but some people don't (routing sometimes could be weird etc., haven't tested extensively the new version yet) . It has most functions, a few are not there, but does a good job and has very good graphics, imo that is. POI's are ok, not perfect, but you could use it together with google maps, e.g., to find a POI if not available on the Nokia Maps (that of course would have some higher data usage). I prefer maps that could be stored locally (as nokia's maps, garmin, tomtom etc.), since they incur no data charges and could be used out of gsm coverage. Nokia's maps though are subscription based (from a month to a year). I got a 3-year North America maps subcription for v1, which was at the price of a 1-year now (it incl. south america now too). I had issue with maps 2.0 with the license and Nokia CSRs weren't very helpful, but to my surprise since 2.0 moved out of beta, it automatically activated the licence on my E71 based on my SIM and gave me the remaining 2.5 years (didn't actually expect that).
Screen is smaller on the E71, that could be an issue for navigation, though it looks sufficient, if not perfect. There's no substitute for a dedicated Nav system, imo (I've used my N95 for that with my old car, and it did a decent job though).
I'm going to Montreal next week (1,000 kms one way drive) and might test it a little more. I have a 7in touch-screen built-in nav system in my car (with sirius trafic info) and don't really care to use my phones' navigation much (still like it as a backup and just in case). I would def use the E71 in Montreal in walking mode with Nokia's maps and see how well that works.