Overall, the non-IS version will deliver a bit better IQ. But...a shot blurred by camera shake will have bad IQ. So...how important is IS? You've rented the 70-200 II before - I'd say look over your EXIF of shots with that lens, with an eye to shutter speed. If you're often shooting slower than 1/200 s at 200mm, etc., then you're benefiting from IS and the original IS version of the lens is likely a better choice for you.

As for weather sealing, the 5D isn't a sealed body so unless you're planning on moving to a 5DIII that's a lesser consideration. Still, I suspect the IS lens will be a better option for you.