The Delta Wing is based on a low drag concept so it's fast (for the power) down the straights at Le Mans.
The questions are:
1, Is the Deltawing shape actually better aerodynamically than a "conventional" car?
2, Is it advantageous enough (if at all) to overcome the inherent cornering disadvantages of the three wheeled layout (given equal rules, as opposed to the weight advantage that we'll see at Le Mans this year)?*
* -This reminds me very much of motorbikes vs. cars comparisons. Take a caterham superlight; 200bhp, 550kg ish (including driver) and compare it to a BSB championship Superbike; also 200bhp, but only 270kg with rider and a really small frontal area... which is faster around the track? Actually the lap times are basically the same at whichever track you look at, even high speed tracks; so despite the extra weight, and much bigger frontal area the inherent advantages of a rectangular wheel layout are so great that it makes up for the huge weight and aero advantages of the superbikes...
....and that's the problem with the Delta-wing -it doesn't have the inherent advantages of the rectangular wheel layout (granted it should be better than the 2 wheel layout above).... personally I believe the only way for it to be competitive is to artificially skew the rules in its favour (like the AcO have done by allowing the Deltawing to run at a much lower weight than the rectangular cars)....
The good news is that we'll be able to make some rough calculations of the Delta wing drag coefficient after Le Mans qualiying -assuming that we can believe the power output figures quoted (I wouldn't be surprised if the Deltawing ends up turning up the boost on its engine above the officially quoted figure... or am I just too skeptical?!), so that should help us answer Question 1....
