I can confirm that the problem can be fixed by disabling ASPM. I downloaded e1000e-0.4.1.7.tar.gz from sourceforge, modified it to build with kernel 2.6.27, and verified that the latency problem still occurs. Then I disabled ASPM for my chipset (Intel 82573L) and since then I've got stable ping results.
I can confirm that the problem can be fixed by disabling ASPM. I downloaded e1000e- 0.4.1.7. tar.gz from sourceforge, modified it to build with kernel 2.6.27, and verified that the latency problem still occurs. Then I disabled ASPM for my chipset (Intel 82573L) and since then I've got stable ping results.