I'm a long time Shimano rider, but my current main ride is Sram Force. My back up bike is Shimano Dura Ace 7800.
I'll back what sstorkel has said above.
Both work well. The change of level style and actuation only takes a short time to get used to.
Shimano is a lot quieter and smoother in the shift lever action. Force is a bit 'clicky' or 'notchy' in your finger tips - probably due to the Double Tap.
Performance? The limiting factor on my bike is sitting on the saddle....
I swapped because I was building a new bike and the Force was the best 'bang for buck' in terms of weight and bling when purchased as a separate group in a box (value on a pre built whole bike is another thing).