While I agree that CentOS6 is the new and better OS I should say that it has several serious problems (bugs) that have been bugging us for several months to the point the we began considering going backwards to 5 which was solid as rock from day 1. Apparently these bugs (related to the kernel and possibly nfs4) have been fixed in RH EL6 but only to those that maintain a service contract.
Are there by chance bugzilla entries for those? Just out of curiosity - NFSV4 is an area of interest to us, in the future.