Upgraded to Swiftech MX462: not much difference?

I have a Asus A7V333 board with a Athlon XP 1800 (AGOGA stepping) chip. Basically I had been able to overclock it from 1553 to 1665 using the frontside bus. The temperature normally runs around 40-44 C at 1.85 volts at load. I had used a OCZ Goliath SE and Globalwin CAK38 heatink. The OCZ used a OCZ fan at 3000-3700 rpm (80 MM) and the other used a Globalwin 6800 rpm fan (60 MM). After switching between the two I got the same results. I could not overclock it higher without it locking up in certain programs. So I upgraded to the Swiftech heatsink. Not only is it one of the best designed heatsinks but it cost me a lot. It uses a Delta 80 MM 5000 RPM fan at 69 CFM. Even with this fan I still get the same results. All three I get the same load temperatures of 40-44 C. I tried switching fans to pull air off the heatsink but that made no difference. I have lapped the northbridge heatsink and added some better thermal paste but that made no difference. I followed the directions for the Swiftech heatsink carefully and made sure the mounting screws were tight. Any suggestions?

are you using good thermal paste?
do you have ample case cooling?
did you lap the heatsink?
did you use enough thermal paste?
did you use too much?

I used arctic silver 3 thermal paste. I only used a thin layer on the chip. There is no need to lap this heatsink since it comes machine lapped/polished from Swiftech. I am using a Enermax 120 MM 2700 RPM fan right above the heatsink and another in the front of my case. I was thinking it could be the stepping of the chip......