New graphics or laptop?

In my current situation im going back and forth between my home in reno, and my home in Las Vegas (dual custody). I have a desktop here in Reno, with an fx-8350 processor, and a radeon hd 7870 gpu. When in vegas, I have a desktop with an fx-6300 and radeon HD 7770. In vegas I spend every single day with my girlfriend. We are both gamers. When I am gone, in Reno, I have my desktop and she has hers. But when we are together all I have is a macbook pro for her to be on (which obviously can't handle many games) while i'm on the desktop, or vice versa. I could either get a nice used laptop for around $500, with 8gb ram, an i7 820qm, and radeon 5870 from a friend, or I could get a gtx 770 with titan cooler, and in turn, get the 7870 to put into the desktop in vegas to replace the 7770. Also, both desktops are running at 1920x1080. What are some of your opinions as to which i should do? (I know there were other specs that are important that i could've included, but I am to lazy to list them.)


Also, some elaboration would be very helpful :)

Ever heard of a ViDock? It lets you attach a GTX titan or other GPU to your macbook pro, the mac must have the very latest OS X, and prefferably nVidia web drivers.