Help a senior citizen

Retired but working part time. Limited income. Much soul searching and I balanced economics with "you only go around once" and "what the hell". Throwing caution to the wind I have ordered what I consider to be the best camera I will ever have the privilege of owning, the D800.

I will probably replace some of my DX primes with FF primes (50 1.8, 35 1.8(or 28) and 85), but I do want a walk around zoom.

I was pricing the 24-120 f4 and it is more then twice as much as the 3.5-5.6. I generally shoot in very good light (low desert dweller), so if I generally shoot at or about f7.1-8 am I really gaining anything with the f4 for another $700-$800.? Any other recommendations regarding walk around zoom?
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http://digitalphotonut.zenfolio.com/
http://www.flickr.com/photos/61931648@N02/?saved=1