[CentOS] How can binaries be different when package versions are identical? (mkfs.ext3 on CentOS 5.4)

Situation:  two similar servers, both with CentOS 5.4 64-bit.  Making
an ext3 filesystem on one takes seconds, on the other minutes.

Partition Size    Server 1     Server 2

1 GB                  0.7 sec       0.3 sec

4 GB                  2.5 sec       1.2 sec

40 GB                15 sec        13 min

WTF

e2fsprogs RPM is e2fsprogs-1.39-23.el5 on both systems
mkfs --version reports "util-linux 2.13-pre7" on both systems
mkfs -V reports the same on both systems (mke2fs 1.3 (29-May-2006)
Using EXT2FS Library version 1.39)
file size on mkfs and mkfs.ext3 binaries is identical

However, checksum on these binaries differs across servers, and "cmp"
reports files are different

I took "mkfs" and "mkfs.ext3" from server 1, put them on server 2, and
got an improvement:

40 GB                15 sec        3 min

Just out of curiousity, I ran "rpm -V e2fsprogs" to see if rpm would
pick up the difference and sure enough, it complained mkfs.ext3
changed.

Both of these servers have CentOS 5.4; Server 1 was installed in Dec
2009, Server 2 in April 2010.

I'd like to:

(a) account for the difference in the binaries, and
(b) see if something else is different that I can make the same to get
the mkfs.ext3 time down to 15 sec on both systems.

Solving (a) should shed light on (b).  Any ideas?

Best,
Aleksey