I'd buy quality first over a lot of X's. A 9X or 10X scope is adequate and 50mm scopes are generally lower quality than 40mm scopes in the same price range. I cannot think of a good reason to use a 50mm scope.
There are a lot of very good 3-9X40 and 2.5-10X40 scopes out there under $500 that will be far better optically than what you are considering. Of course they don't have the tactical look.
http://swfa.com/Zeiss-3-9x42-Terra-R...pe-P61667.aspx
Zeiss recently replaced the Conquest with this model. You might still be able to find a Conquest for around $300
http://swfa.com/Leupold-35-10x40-VX-...pe-P12647.aspx