It’s actually being exported into 16:9 anamorphic, so shooting it in respects to 4:3 shouldn’t be a real issue. I have heard that if you nest the hd sequence into an sd timeline, you can render it and then export it just fine. I have also heard that media manager might be able to compress all the media before it hits the bin. Still, I am unsure the best way to go about that.
Personally, I have shot on neither, but I believe the lens is considerably better on the ex1. I’m sure you can get the job done on the 100 just fine, but if you have the means to shoot on the ex1, I think you should.