why not pop along to your local Sony Centre, try & see them both in action. Check out the Sony website for facts & figures.
Looking straight on at the 40" 703 model I thought the picture was excellent with HD material. I never looked at the picture from the sides as I always watch my tv sitting directly in front of it. It`s a fantastic looking set.
Only got to see a 32" 503.
As yet there have been no reviews of the 703 - if I had the room for a 40", the 703 would definitely be on my shortlist.