Well, I'm not expert but as a reference I would tell you that the MareNostrum (a supercomputer at my University) runs Suse linux...

What GoinEasy9 said, try Scientific Linux. It is a RHEL derived distribution maintained by the high energy physics community and is widely used world-wide for scientific research, data acquisition, data analysis, and just general use. My wife even uses it on her Toshiba netbook computer (she is a particle physicist at a major accelerator lab).

What are you trying to do? Single desktop? Server? Cloud? If you are looking into doing FLOPs then you should look at what this Professor did with just a few PS3s and Linux. Or, password crackers use Linux on a single gaming machine while running SLIed graphics cards for the GPUs (ref:Using multiple graphics cards as a general purpose parallel computer: applications to computer vision by Fung, J. Mann) I saw it at Defcon cracking away, damn thing was so fast. Its a Black Hats wet dream!