I have the GVS panther 1700w and it is a really good vacuum.
I think most of the time (on domestic) you will only need one motor but good to have the other on standby.
Lee, I used to have the atom and I kept all my carbon poles and purchased the adaptor cuff so I could still use my atom poles, works a treat. I also purchased aluminium poles just for doing bungalows, they are ok but I am too lazy to clamp them all, so I just use them loose. I am very happy with the Panther, so I can only imagine the Shadow would be ideal.
PS. the aluminium poles aren't that great because, although they feel strong, and fairly light, you tend to throw them around and the very end of the pole can 'dent' slightly which means you are now trying to fit a round pole into a hole that is very slightly oval! This can be a pain.
PPS I always fully extend the extension lead and use a circuit breaker on the extension lead reel, so you should never trip the custys electric, should a problem occur.