Finally a stable connection
As I previously recorded in the posts here and here, my network interface card under Windows 7 started to drop the complete traffic whenever it got stressed out with network traffic. Heck, sometimes not even when stressing it out. Digging through various fora I came to the Nvidia forum again and found a thread that mentioned a Microsoft Knowledge Base article that instructs in turning off receive-side scaling.
After turning said option off and stress testing the link for a few hours I did not experience any drops. So this might actually finally be the stable connection I am looking for.