LEL2013 will probably have a different route to LEL2009. It'll be more to the East in the flatlands (South of York) and there's talk of going North via Eskdalemuir but coming back South via Moffat and Lockerbie.
The Barnard Castle - Alston - Brampton - Longtown section should still be there, it's simply one of the best bits of LEL.
I rode the LEL route one way in March 2009 to get an idea of what to expect on the real thing. GPX tracklog was this:-
http://www.bikely.com/maps/bike-path/266092
Note that I had to make various adjustments in order to fit in accommodation and food as I had to rely on commercial controls rather than the primary schools and village halls used on LEL. Also made some adjustments so I could ride each day as a DIY Audax and claim points for the rides:-
* Started from home in Putney rather than in Cheshunt
* Day 1 was a DIY 300km Audax to Thorne (
Travelodge at M18/M180 services accessed via a side road and along the side of a field)
** First 150km on my own until meeting up with a friend near Peterborough who joined me for the rest of the ride.
** Went via Bourne rather than Thurlby. Also went through Lincoln (LEL2009 went on a big long detour out to Wragby to add some distance)
* Day 2 was a DIY 200km from Thorne to Alston (stayed in a B&

.
** Went via Scotch Corner and the A66 rather than the Aldbrough St John
* Day 3 was a DIY 200km from Alston to North Berwick (Dalkeith/Edinburgh wouldn't have been 200km so I needed o go further.)
** Followed what was the proposed LEL route through Canonbie and Claygate, which was much hillier than the final route that simply used the A7.
** GPS ran out of space (10,000 track points) on the A7 towards Edinburgh.
** Finished in North Berwick and got the train back in to Edinburgh. Stayed in the City Travelodge near Edinburgh station. Up the next morning and on to a train back to London.
It definitely helped me riding the route in advance, but it take a bit of the shine off the actual event as it wasn't all new to me. Doing the same roads twice (or 4 times for the shared bits) will only make this worse.
LEL requires 288km a day minimum (24 hours * 12kph), so it may be worth booking accommodation to fit a schedule based on that. Something like:-
Day 1: 300km to Thorne
Day 2: 300km(-ish) to Longtown or Langholm
Day 3: 300km(-ish) up to Edinburgh and back to Alston
Day 4: 300km Alston to Lincoln or Bourne
Day 5: Finish off whatever is left.
Remember that 300km in a day isn't hard, but doing almost 5 consecutive 300km days with less than 3 hours sleep each night makes it all a bit harder.
Note that Cheshunt to Dalkeith isn't quite 700km. LEL2009 was brought up to 1400km with an extra 60km or so by adding in a checkpoint at Wragby after Washingborough on the way North. LEL 2013 will be making the route at least 1400km in a different way.
One word of warning: After you've got over the first few lumps in Hertfordshire the rest of the southern section (Gamlingay to Thorne) is frighteningly dull, but it's good for building up a time buffer. It starts getting much more interesting after Middleton Tyas.