He is building the canon 1701 from what ive seen, the 2009/darkness enterprise isnt considered canon, because it is the result of time travel, thus making it a parallel universe.
Also a 725 meter enterprise would dwarf most \"prime universe\" vessels, as they are mostly in the range of 200~500 meters, only 2 canon ship classes have breached that barrier, namely the Galaxy and Sovereign Classes.
For comparisation:
Enterprise 1701 (TOS): 289m
Enterprise 1701 (Refit): 305m
Enterprise 1701 (New): 725m
Quite a jump, isnt it?
Also, the CGI in the \"new\" movies screwed up most size comparisations, making it almost impossible to determine the actual size of the new enterprise.
Source of all facts:
http://www.ex-astris-scientia.org/
About the Enterprise size controversy:
http://www.ex-astris-scientia.org/articles/new_enterprise_comment.htm#size