Re: Vortex Diamondback 4-14x40 AO vs Non AO
I will say yes, you may be shooting 200 now, but if you plan to take that rifle to further distances, the AO will allow you to reduce parallax.
As for budget, I suggest you purchase the highest quality scope you can afford. If you are on a budget it is best to make every dollar count. If you rush, you will get a scope on your rifle, but it may only frustrate you when you are at the range or in the field.
The Diamondback is a decent scope and is made in the same place and carries the same warranty as the viper, but the Viper has the side adjustment and a step up in glass quality.
Leupold, Redfield, Vortex all have nice scopes for those on a budget. The great thing is if you purchase one second hand it still has a lifetime replacement.
Keep an eye on the SWFA sample list, they will sell demos and buyback scopes at greatly reduced cost.
http://www.samplelist.com/ViewProducts.aspx
Also for Nikon there is a promo going on their BDC scopes.
http://www.nikonpromo.com/assets/bdc/bdc_days_web_form.pdf
I have owned a few Nikons, they have nice glass, but I have moved on. Never was a fan of their tight eyebox.