Nashd – some more of me thoughts….
Re. the Edge – I have a 705 which I use for “training” (ha!) and the occasional Audax. I find it very irritating that I cannot suppress the road and street name labels, which obscure the map with irrelevant info just as I’m approaching a junction. There is a setting to show “less detail”, which reduces this but unfortunately it also causes the small roads and lanes to disappear too, at least until you’ve zoomed in very closely (and then lose the “overview”). In practice, I find the Edge a pain to navigate with in areas which I’m not familiar with.
The power duration is an issue with the Edge but others have managed very well with external power packs. I haven’t tried these and I’m cynical about my ability to rig something up which is weatherproof. It’s also more clutter on the bike and more vulnerability to vandalism if you want to pop into a shop or café and don’t feel comfortable leaving the kit on the bike.
If you decide to go for the City Navigator, be careful. I THINK that if you obtain the mapping via a download or on a DVD, when you install and activate it with Garmin it gets permanently locked to whichever hardware you have; thereafter, you cannot transfer it to a replacement unit even if it’s also a Garmin. The way to get the mapping is to buy the pre-loaded microSD card, which can be transferred between (Garmin) units. (I believe I have this correct but PLEASE do your research and check this out before buying; get it wrong and you may have to repurchase the maps if you change units in the future.)
More skilled individuals sing the praises of Open Street Map and similar open source freeware. I have no experience of any of this, so cannot comment.
I don’t believe any unit is perfect yet for cycling in that it will do all the “bike computer” (performance data, heart rate, cadence, etc.) whilst simultaneously delivering good navigation (big screen, rolling OS mapping, car satnav auto-routing that works for a bike).
From the way you’ve spoken, it looks to me as though the Extrex is the way for you. Your budget will determine whether you go for the modern OS mapping capability or not. For me, I wouldn’t be without it; the ability to see on an OS map the classification of the roads ahead (red, brown, yellow, etc.) beats the City Navigator hands down; on the City Navigator, all roads are just brown lines, whether they're A-roads or bridleways. With the OS mapping, when I zoom out, it changes to the 1:250,000 road map, so I get a usable overview when navigating on the fly. When I do that on City Navigator, all the small roads disappear and I’m lost; it’s just not workable comfortably. If however, you are happy to continue to do part of your navigation with a paper map, then the City Navigator can be used for the job.
You pays your money and you makes your choice, as ever! Good luck!