Tim
I think you will find that whatever machine you use it will clog up pretty quickly.
If you use a larger machine with a paper bag, you will end up wasting more of the bag than a smaller one. In my experience with brick dust on builders cleans a vacuum cleaner will lose suction pretty quickly. The henry is an ideal size for your needs, the trick is to make sure you dust the main filter regularly even if it takes longer to do the job, as this will extend the life of the vacuum. Also you will need to allow for the use of more paper bags. If you are buying the bags in bulk you should get a good discount.
Derek