I'd downgrade to a lower level. Forget the lightweight stuff if you are going for a year-plus. I've experience with both SRAM and Shimano at the levels you are discussing, but for my purposes, I prefer the strength and durability of the lower levels, such as LX or even Deore. The lower level stuff also is cheaper so when you inevitably come to replace it, your funds won't be drained by the expense of high-level componentry. Having said that, I slightly prefer SRAM over Shimano.
One thing I did notice when I broke the rear dropout of my touring bike and rode on for 400km without realising, is that when the chain derails in between the spokes and XT cassette, it becomes a mighty difficult chore to get the chain out from behind the spider on the roadside with limited tools.
Oh and also with the spiders, you can't mix and match cogs as you could with the other models. It's probably not that important to you unless you want to go the Sheldon Brown/Harris Cyclery route with a better range of cogs.