  Very massive high redshift clusters can be used to constrain and test the
Lambda CDM model. Taking into account the observational constraints of Jee et
al. (2009) we have calculated the probability for the most massive cluster to
be found in the range (5.2-7.6)e14 M_sun, between redshifts 1.4-2.2, with a sky
area of 11 sqdeg and under non-Gaussian initial conditions. Clusters constrain
the non-Gaussianity on smaller scales than current cosmic microwave background
or halo bias data and so can be used to test for running of the non-Gaussianity
parameter f_NL.
