Feck me, what is the speed limit? The speed limit is the speed posted on the signs. For most non-motorway roads in France it is near enough the same as it is in the UK, 60 MPH give or take a touch. Through towns and villages? Rough rule of thumb, 30 give or take a gnat's cock. It is up to you how much notice you take of these signs and limits as you hoon your awesome steed in the direction of the white cliffs of Dover and safey.
What are the roads like? Look at the fecking map. Still not sure? Look at Google fecking street view, it will show you every fecking manhole between Aberdeen and Nice.
This is the return leg of your adventure, is it not? It's safe to assume that after plotting 2000 miles you'll know what the roads are like up to this point, no? Yes? Great, mate. You'll know what to expect, won't you.
Now employ some imagination, a bit of time with a map, avoiding the motorways and work something out that will get you from A to B in under six hours. Direct, on dull motorways it's 260 miles, or a bit under 4 hours. Motorways? You shit 'em, as Harold Shand was prone to say. So, it's awesome roads time: If you ride at a true average speed of a mile a minute, that is 360 miles. I guess you won't do that. If it's half a mile a minute, halve it. Now look at the map... How are YOU, not me, not the man next door, going to do it? Destiny lies in your hands, bruv.