I know it may seem ridiculous but I got my info from this site.http://en.wikipedia.org/wiki/Optiplex
Anyway its says the chipset is only a 915, as far as I can tell that's even older than my Dimension E520 which uses a G965. That wouldn't support PCI-e 2. It wouldn't just be a bottleneck the highest CPU it could go would be a Pentium D, and that already is a bottleneck as it's a sub-par dual core CPU. I would know I own one.