I would go for the Sebo X4. It's a really sold and powerful machine.
People here have had issues with the Miele hoses kinking up and staying that way, so unless they've fixed that problem, there is no reason to spend that much for a machine that is going to have that happen. I guess not everyone has had that issue, so that has to be taken into consideration.
I've never found any Electrolux uprights to be powerful, nor especially durable. I played with the Gaudrian in the store the last time I was in that section of town and it really didn't impress me much. Seems very much like the older ones with a different color. I have a friend who cleans houses, and he has a Prolux.... loves it for some reason, though he says using the hose is an absolute nightmare. It comes out and the machine falls over frequently during use. Would you be needing attachments? The Miele and Sebo have them right there, you have to go digging and connecting for the Aerus.
I wouldn't count a long warranty as a selling feature.... Dirt Devils used to have 6 year warranties (motor only, I think, maybe they still do), Orecks have long warranties.... neither brand is especially known for quality or performance.... I think that manufacturers offer long warranties as a selling feature, knowing that most people will toss the vacuum and buy a new one when it breaks. I guess you'd be a little more hesitant with a 1000 dollar machine.