Excellent answer, both are chronographs. I‘d go for the DC86, all in all the more advanced Damasko movement.
Of course it does, their C51-6 implements more than a 7750 Si. The main technical gimmick is the implementation of a jumping 60-minute hands out of the center the center. That’s something a plain 7750 can’t feature. The more you get, the more you pay.It cost more than the SI.