Not tried it on the tenere yet but from experience with exc I found a smaller front sprocket worn faster due to the increased angle the chain runs. I also found that this worn the chain wear guide on the swingarm faster too.
But I aslo use the swop the front first to prolong the life and chain and rear sprocket is normally still in good nick.
Personally I'd go for a steel sprocket not an anodised one as its not like you need to save on weight ie not being raced.
I went from using a smaller front to a larger rear, but that does mean chain length will have to be increased to suite.

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