I bought the 13" 8/256 yesterday, coming from a 2010 15" with dual drives (SSD + HDD). I then got a 4TB USB 3.0 WD My Book, dumped the HDD from my MacBook and it benchmarks faster than my old internal drive did! I just ran a Call of Duty session off of the external drive, and it performed just fine. Especially since it was importing a thousand pics into aperture and importing iTunes at the same time
I'd grab a USB 3.0 drive to store your big apps, and all your media on and call it a day. I plan to keep the external drive at home with my big stuff, and just keep the OS and main Apps on the SSD. And leave just enough space to import stuff when I'm on the go, then move it later. You can also install Steam on the internal drive, and have it store game files on the external. Worked great for TF2 and Portal 2.
As for the games, I don't do much (have a PS3). But I find running them at medium high at 1280x800 works just fine. I did run COD 4 and Half Life 2 at 2560x1600 just because, and it worked alright. But everything was tiny, lol. Newer games would kill it at that res though. When it's on my external monitor running at 1080p most games I play run just fine on the Iris. Pretty impressed with it coming from a 9400m then a 330m.