More Q's does expensive gear or brake cable make a diff?
Personally I believe in using the best gear cables I can to reduce friction and ensure a nice crisp shift. And certainly, if you're using an under bar tape Shimano STI system you need to do everything possible to reduce friction to make it play nice. That means expensive cables .. Go Dura Ace if Shimano is your thing and you want to keep it in the same groupset family.
Personally I believe in using the best gear cables I can to reduce friction and ensure a nice crisp shift. And certainly, if you're using an under bar tape Shimano STI system you need to do everything possible to reduce friction to make it play nice. That means expensive cables .. Go Dura Ace if Shimano is your thing and you want to keep it in the same groupset family.