SGI IRIX 5.3 or 6.2 best for xtallography software?

[Thomas Earnest]

having successfully installed CCP4, X-PLOR, RAVE, O, HKL,
and others on a R8000 running IRIX 6.1, i do not see any problems.

IRIX 6.2 will be the cross-platform version of IRIX, and SGI assures me 
that everything which runs on 5.x and 6.1 will run on 6.2 on the R10000
(i will soon test this). 

thus i would say you made a good choice with the R10000 and IRIX6.2