I was thinking about a tablet, or maybe a 2-in-1, but I think I would rather have a nice 15" or 17" display, full HD. Since I have a pretty powerful rig streaming the games at 1080p 60 FPS, it's only right I have a client that can handle it.
I'm thinking a used/refurbished Dell XPS M1710. Full 1920x1080 resolution, 17" screen, Nvidia graphics, a dual core processor at 2.0 ghz and a few gigs of RAM. Should be enough to handle the job nicely, right?
To tell you the truth, I think the biggest issue you may have is not the hardware itself. If you're using a wireless connection, just to test, try connecting the laptop wired to the network and see if the speed issues remain or not. If they remain then yes, could be the hardware capabilites, but maybe it'll work fine, in which case it's a matter of wireless vs. wired and not much to do with decoding speed.