[CentOS] Strange performance issues under CentOS 5.1

I am still running CentOS 4.6 on our production systems, but I am  
starting to plan the upgrade to CentOS 5.1.  I have one test system  
running 5.1 that is the exact same hardware configuration as my 4.6  
test system.  One of our builds runs about 6 times slower on the 5.1  
system, even though is uses less overall CPU time.  I first suspected  
something wrong with the disk, but the results from bonnie++ show  
that the 5.1 system is slightly faster:

   Version  1.03       ------Sequential Output------ --Sequential  
Input- --Random-
                       -Per Chr- --Block-- -Rewrite- -Per Chr- -- 
Block-- --Seeks--
   Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec % 
CP  /sec %CP
   centos4.6       16G           35933  10 21301   5            
46507   6  41.8   0


   Version  1.03       ------Sequential Output------ --Sequential  
Input- --Random-
                       -Per Chr- --Block-- -Rewrite- -Per Chr- -- 
Block-- --Seeks--
   Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec % 
CP  /sec %CP
   centos5.1       16G           42015  14 21179   5            
49863   4  91.6   0

Then I ran the build with "/usr/bin/time --verbose", and here are the  
results (first 4.6 then 5.1):

         Command being timed: "make"
         User time (seconds): 32.15
         System time (seconds): 3.52
         Percent of CPU this job got: 99%
         Elapsed (wall clock) time (h:mm:ss or m:ss): 0:35.88

         Command being timed: "make"
         User time (seconds): 22.05
         System time (seconds): 3.11
         Percent of CPU this job got: 11%
         Elapsed (wall clock) time (h:mm:ss or m:ss): 3:31.35

As you can see from the above, there is a lot of idle time on the 5.1  
system.  Finally, I ran the build with "strace -c", and here are the  
top ten lines of that output (again, 4.6 first and then 5.1):

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
  53.81   16.804147       54916       306        58 waitpid
  34.75   10.853461       82851       131           wait4
   5.29    1.650844           9    177706    154581 open
   1.61    0.503701          15     34408           read
   0.91    0.283706          15     18607           write
   0.60    0.185894          12     14919     10364 stat64
   0.52    0.163340          10     16495      9079 access
   0.47    0.146933           7     20581           mmap2

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
  60.07   15.173924       52687       288        58 waitpid
  38.50    9.724412       83831       116           wait4
   0.54    0.135194           7     19199     10705 access
   0.36    0.090850          54      1681      1334 execve
   0.27    0.067686           5     14423     10570 stat64
   0.11    0.027676           1     24832           read
   0.09    0.022339           0    155810    135765 open
   0.03    0.007617         159        48           unlink

Any suggestions as to what could possible be causing this?  I am  
fresh out of other ideas to try.

Alfred