Given these choices for my D40, which would you buy?

Tamron 17-50mm f2.8
Sigma 18-50mm f2.8
Tamron 28-75mm f2.8

Sigma 30mm f1.4
Sigma 50mm f1.4
Nikon 50mm f1.4

all in the $400-500 range.

Or unless you would recommend me something else that is in THAT PRICE RANGE and AUTO FOCUSES on the D40.

I'm looking for speed, so it's either I go zoom and settle for 2.8 or prime and get 2 more stops.
I really do like my kit lens though, so maybe zoom is the way to go.

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