Which filesystem for 40000 RRD files

Hi all,

I use MRTG where is about 40000 targets (RRD files).
Every RRD file have about 100k.
I have always troubles with I/O performance and I have idea if another 
filesystem will be better for me.

I use EXT3 with these parameters.
Line form /etc/mtab:
/dev/sda4 /usr/local ext3 rw,noatime,commit=120 0 0

I have CPU 2x Xeon(R) CPU 5160  @ 3.00GHz and 8GB RAM.
2x SAS 15000RPM disks in a hardware mirror.
I have CENTOS 5 based distribution.
Have somebody idea that with this distribution is better to use EXT4, BTRFS or 
XFS for bigger performance? Or it is better to stay on EXT3?

Thanks, Pavel