Is there a difference? Yes and its off the charts when it come to stimulating the chest region. I know you feel it more in a fly movement right? Is it more strain, and stress that equates to the feeling? That’s how most would judge the validity of a specific exercise…ALL FEELING! The internal forces trying to overcome external application is all it is. A chest press is far more effective (with dumbbells) Vs, a fly. Let’s not mention the straight bar bench. The straight bar is far less stimulus than both combined.