New 2012's Sora 3500 vs used 2003's 105 5501
After making it to Norway with the Sora groupset, now I regret the change. As far as I remember, the original 105 was faster and I would guess, reliable enough.

I am used to good derailleurs, even though they could be old. For my commuting bike I use a Shimano 600 tricolore from the late eighties and for my road bike I use a Shimano Ultegra from the late two thousands. Once I finished my trip and came back to my other bikes, I realized they are way better, and still reliable even though they are old.

Moral of this story: for shimano at least, it's better old and good than new and bad.