the reviews say it is really heavy?
Store reviews are not to be taken seriously - that really isn't a good way to judge a product.
For xeon is better take B-75 or H-77 MoBo.
I really dislike B75 - it has very limited expansion options and it also has outdated ports that you will never use. It's meant for business machines - not for consumer / gaming rigs.
should i get the diamond radeon 7970 ghz
No - stick with the Vapor X, Diamond isn't really a recommended GPU manufacturer.