The galaxy cluster Abell 2744 is not only one of the most massive objects in the current Universe, it also contains eight very massive (M > 10^14 Msun) substructures within a radius of 1 Mpc from the cluster centre. It thus provides an excellent probe for the Lambda-CDM model. However, the comparison of masses obtained by gravitational lensing analysis with those obtained in simulations comprises many difficulties, such as line-of sight projections or the choice of cosmological parameters in the simulation. I will shortly present ways how to make those masses more comparable to each other and how to include biasing effects. Using these results, I will then summarise the search for Abell 2744-like clusters in the Millennium XXL simulation.