There is enough room in the world (and on your iPods) for both DT and whatever projects MP embarks on. Dream Theater is not just Portnoy's drums; it's Petrucci's guitar, Rudess' (and if you go further back, Sherinian's and Moore's) keyboard, Myung's bass, and LaBrie's vocals. Just because their drummer has left doesn't mean the whole DT sound has gone forever.
So I'm sticking with DT and Portnoy. I'll admit I'm not that big on A7X, but I love Transatlantic and hope they'll bring out more material in the future.