There are five distributions for SGI machines:

 5.2 was compiled on a R4400 Challenge using -mips1 flag.

 5.3 was compiled on a R4600 Indy using -mips1 flag.
     This version should run on all SGI's with IRIX version later than
     5.3.
    
 6.0 was compiled on a R8000 Indigo2. 

 For optimized performance:
 6.2-n32 was compiled  on a R10k with -n32 -mips3 flag. (should 
        run on 6.2 R4400 machine with -n32)
 6.2-64bit compiled on a R10k with -64 -mips4 flag

 If you're not specifically looking for optimized performace, you
 should get the 5.3 version, which should run on all SGI machines
 (provided OS version > 5.3)