I had ESM 2003 SP2 on my BES 4.0.3 and RIM said they were pulling back support for it. They did originally, but suggested moving the ESM down to SP1. I did this in a round of troubleshooting some MAPI issues. Although that in particular did not fix my problem, I have noticed a small performance increase since making this change. Not sure if it has anything to do with it, but my BES seems to run better with ESM SP1 versus SP2.
Current - 8700g TMO
Previous - 7280 AWS, 7730 TMO, 7290 TMO
Long ago - 950 model (still have it)