Upgrading Nikkor 18-105

[Primoz]

I am thinking about upgrading my kit lens Nikkor18-105 for something sharper, faster and with a generally better image quality.
I like shooting landscapes, but I wasn't considering an extreme wide angle, since I am also shooting a lot of events and will be using this lens for general purposes also.
I was looking at the Sigma 17-50 f2.8, which I guess is a good, fast general purpose lens, but I'd like to know, if it is also a good performer for landscape shots at 17mm?
Is 17mm wide enough for a more serious landscape photography? I am also considering getting a polarizer and an ND grad filter sistem (probably Cokin or Lee) and don't know which holder size (P or Z??) to get for this particular lens. Any ideas?

I thank you for your help,
Primoz

 

[nick_cool]

I want to do the same.

I am thinking of either a Tokina 10-20mm or a Nikon 24mm.

Main concern is speed as well as do not break my pocket.

Nick

PS go ahead with the ND grad filter system Cokin, I love it.