1 when selecting the closest entry point does it always select forward no matter what, in other words if you were at more than half way along the route and you left the route, and then wished to return, but your only point forward was the end of the route, and there were closer via points nearer to you going back towards the start, which would it choose when you hit closest entry point.
I am not sure. I tried a few alternatives - forced a route with an 'n' shaped kink in it which came within a hundred metres or so of my location, with a Via Point just slightly upstream of me. It wouldn't choose that as the Closest Entry. From the experiments I carried out, all of them chose a route downstream - ie in the direction of travel of the route to the final destination. The satnav does know which way the route is heading at all times, so it is possible that it checks this before it even starts to look. I don't think it will choose a point going back to the start even if it is closer - that was what I was testing. Sometimes that would be the best option to get back onto the route.
If there are standard shaping points (ie not ones that are Waypoints) on the route from where you are to the end, it will ignore those and take you straight to the end. See my answer to your question 3.
2 If you were to stop while actually on the route, switch the unit off and then a while later re start the route what would happen, (what does the unit ask).
I haven't got a clue about that, but I can make a pretty good guess. Sorry - I can formulate an intelligent hypothesis.
When the satnav restarts, it has kept the route in the same state as when you left it, and it even knows your position before it gets the satellite signal. (Unless you have moved somewhere else, in which case it knows where you were when you turned it off.) It also know which section of the route you were in, so when you restart it will try to get you back to the next routing point in the route list. My guess is it would continue to naviaget you to the next point on its route. It may skip shaping points silently if you get onto a later section of the magenta route, but it will not skip Via Points silently. You need the Skip button for that. That is my experience with the 590 and the 595. (The 595 has autoskip). The XT has the autoskip feature too, and I have tried that out on the XT and it behaves in the same way as the 595 - so far.
I can see very little difference between the XT navigation and the 595 - but so far this can only be an educated guess. Educated or not, it could prove to be wrong. As time passes and when I can try it on the next shopping trip, I will know a bit more. But its nice to have a theory so that I can create a test to support it, or to prove it to be wrong.
3 Have you done any real world testing of the unit or has it all been done in simulation.
Very little real navigation testing - but I discovered from the 590 and 595 that some things you CAN test without moving anywhere. Take these examples (which relate to your question 1.)
The left picture below shows the Zumo screen zoomed in to show the complete route, but I have zoomed it in to show the last 3 shaping points and the finish point. This is just after the route has been selected. On the XT there is a GO button and a MAP button to its left. This is where this map has come from.
So in this 450 mile trip, the last the last Via point has been passed, the route behind is south and east and I have positioned the motorcycle off route, just up the M6.
Ahead of the motorcycle - to the east and south - there are three more shaping points ahead, and the finish point in the bottom right corner.
So I am about to set off on this route and select Go and Start. Except in the arm chair there is no need to press start - as soon as you press go, it asks for the next destination, I chose 'Closest Entry Point' and it calculates a route - and then displays the map, with a START button in the bottom right.
The image on the right is what it has created. Note that it has missed out all of the blue circle shaping points, and in fact they do not feature on the map at all. Instead it has plotted the fastest route to the next valid Entry Point - the finish being the closest.
In this second example, I wanted to find out what it would do if I made a Shaping point into a Via Point.
So in the left image which shows the last part of the complete route again, the second point of the three shaping points, east of the bike, is now a flag - a Via Point.
In the right hand image, after selecting Closest Entry Point, In this case it has plotted a route to the flag - and followed the route from there. But intriguing - and not the result that I got yesterday - is that it has also plotted the shaping point to the left of the flag. That point is on the route it has elected to take, so that might be the reason. But I am not convinced by that. I was very clear about what happened yesterday in my tests.
But I update the Zumo software and the maps. I wonder if they made a change. There is no other reason for it to behave differently today, because the route is the same and I carried out the same test, and wrote down the results. Today, the results are different. Hmmm - I need to test this one further. Either the rules have changed or I made a mistake.