Turn-by-turn GPS - Edge 1000, 810 or....?

The 500/510 can be configured to give you turn notifications, at a distance prior to the turn (set by you), if you plan your routes on bikeroutetoaster - no doubt you can do same on 800/810 and 1000. The 500 only gives you a "breadcrumb" type trail to look at though, but I've planned and used it on rides all over in unfamiliar places without problem. If you have these turn directions on then the bleep/turn instruction will pop up regardless of which page of your garmin display you are on. The main difference between this one and the 800/810 version is that can take maps so there is something beneath the breadcrumb line (as said, download the free ones: http://www.dcrainmaker.com/2013/05/download-garmin-705800810.html). This is useful if you go wrong on your pre-set route (the 500/510 is basically useless to get you back to your route) or just want to see what is around you. Obv maps and smartphones can help you in that way, but clearly its a bit easier with it all on your display.

Loads of info (and I mean it, loads!) here http://www.dcrainmaker.com/product-reviews/garmin

If you've got the opportunity to get down to your LBS and look at the screens on the 800 and the 1000 then do so; this is the big difference that you will notice for the requirements you have. The 1000 has a much better screen for navigation, but you pay a premium for this.

Another option for you is the Garmin Edge Touring. Big(ish) screen, but not quite the resolution of the 1000. The ANT+ version has ANT+ (there's a surprise!) so cadence and heart rate etc. shouldn't be a problem. Shed loads cheaper... I've no idea regarding bugs; I've got an old 800 and it's run like a dream since new. Not made me any faster though...

have both 800 and 1000. both navigate well, both get a good lock. 800 is better on
battery life, 1000 is better on failing eye sight
don't use half the 1000 features so normaly take the 800 instead.
create a route, drop it on and away we go ...

I have a mio505 and it's good, couple of points is at roundabouts it can be a bit confusing knowing which exit you need to take. Also I've found the indication for which junction to take can be a bit unclear. It also tells you the distance to the next hill, the average grade and has a course profile which can be useful. The 3xx series is the same as the 5xx models only without wifi upload.

The surprise me feature is good but I am finding the same opening and closing routes being picked and sometimes it can take you to a point on a road then just get you to turn back on yourself.

I've not used a garmin so I can't say if it's better or not.

For 800/810/1000: You can get open street maps rather than paying for the official Garmin ones - the stock maps are next to useless, having only very basic (therefore busy A road) roads. Great how-to selecting and loading these maps is on DC rainmaker blog.

Vote for 1000, Screen resolution and navigation much better than previous models

Another vote for the 800 here

I've had the Edge 500, 800 and now for about 9 months or so the Edge 1000. It is a much better unit in general, not least because of the bigger/better resolution screen and the ability to use both GPS and Glonass satellites, a much more resilient and quicker lock - all of which makes it great for turn by turn navigation. I don't much use the phone link etc features as I'm out on my bike for a good reason - to enjoy the ride!
For those of us with deteriorating eyesight it's great to be able to read the data fields without having to push your nose right up the screen.
It's been my best buy, admittedly not cheap, of the last few years and I can't see myself needing another cycling computer for a long time. Since a firmware update middle of last year I've had no issues with bugs or anything else.

I got an Edge 1000 recently, I have to say I've not really used the navigation features yet - but WRT the reliability I've had no problems - the recent firmware updates seems to have knocked most of those on the head.

Garmin 800 might suit you. It has all the features of the higher models except phone connection. Routing and all the speed power cadence heart sensors easily attached