Landscape lens for D40X

[khendar]

Hi all.

I've been shooting landscapes with my D40X using the standard kit lens for a while now, and I've been thinking about getting a lens especially for sweeping landscape shots. In the past I've tended to cheat and build panoramas in post but I'd like to be able to get a little bit "more" into my single shots.

I was thinking about getting the Sigma 10-20mm f/4-5.6 EX DC HSM or perhaps the f/3.5 but I'm not 100% certain that the focus motor is compatible with my body. From what I've read it SEEMS like it should work but I don't want to fork out $600 unless I'm sure. (just spotted the D40/X lens listing thread. Very handy list )

Is it worth spending the extra $200 and getting the f/3.5 model ? It seems a lot to pay for an extra half-stop.

Does anybody have experience shooting landscapes with this lens on a D40X or similar body ? Is there a better option that I've missed ?

Cheers.