First of all, I am not "bashing" the MRA4, however, to examine the (companies?) claim of flying 6000nm in one go.....
Looking at it as an academic exerise, in terms of simple maths, and ignoring loss of speed in the climb and descent, if the aircraft has an average groundspeed of 400kts, then it will take it 6000/400 = 15 hours flight time to cover 6000nm. That gives you some idea of what we are looking at.
Questions which now need to be asked to decide if it is feasible include at least:
The max flight time for MRA4?
Groundspeed achieved (at endurance speed?)?
Wind component applicable for route?
We'll ignore such things as diversion fuel, etc....
400kts groundspeed (still air) was a good back-of-a-fag-packet planning figure for the MR2 at range speed, and I believe the MRA4 is slower? If you can find yourself a 6000nm long route with about 50kts plus of tail component then I have no doubt the MRA4 could theoretically fly for 6000nm in one go. Could it do it in still air.....I don't know, I don't have enough information!
Overall, it's rather a mote point, with numerous variables. I just hope nobody is producing pretty maps with 3000nm range circles on them....