I fucking love my GH2. I haven't shot with a t3i, but I have shot with a t2i a few times. The layout and image is infinitely better IMO. The flipout touch screen is clutch. With native lenses it automatically zooms in to 100 percent when manually focusing, and with adapted lenses you can just tap the area you want to be in focus. EVF is also nice when theres glare from the sun, or you want a more stable platform for shooting handheld. Plus, you can set it up so pretty much all the important options for video have a dedicated button. Also, you can get a nikon adaptor for those two lenses that will control the aperture for like 30 bucks.
The 2x crop isn't really a huge deal to me either. Your Rokinon 8mm will cover your ultra wide end for now, and later on you can pick up the Panasonic 7-14mm f4. IMO, the virtually unlimited possibility for adapting third party lenses outweighs the limited wide angle choices. Plus it helps you on the tele end of things. For example, my Minolta 70-210 beercan is effectively a 140-420mm, and with the ex tele. conv. on, something like a 350-1050mm.