Hey, I am using the config in my sig and now having the laptop screen opened up while working, it feels like the mac overall is slower. It's not really that big of a difference and might just be in my head but does it really make such a huge difference? I basically just keep it open for skype calls so I have a camera and a mic. Ideally I would want to connect another exact same Dell screen to my rMBP if possible and close the lid on the macbook. Please let me know if the performance decrease is real with the macbook screen open and if i can connect a second Dell screen and how the performance will be. Thanks.