I replacemt all the wheel bearings last year and while checking the bike over its looking possible the sprocket carrier bearing is on it's way out already. Is it possible to kill them in 6000 miles?

Yes, especially if ridden for any length of time with worn cush drive rubbers and/or if the front and rear sprockets aren't aligned straight. If it's got play in it, then it's worth changing sooner rather than later, as when/if they let go they can wreck the sprocket carrier casting.

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Shes a pampered well maintained bike so maybe its my riding style and regular off roading thats killed it.

I've used wemoto bearings but cant recall which supplier they use.

In the past I've used the OE cush rubbers, they don't last particularly well but with regular shim replacement (putting in some rubber shims made from inner tube) you can stretch these out 15 or even 20k miles.

Last time I replaced the cush rubbers with Wemoto ones, new wheel and carrier bearings. I've not even covered 3000 miles and the cush rubbers are goosed, as is the carrier bearing!

Cheap, isn't always the lowest cost.

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Never underestimate the power of stupid people in large groups.

I've heard a few people mention SKF so I may try those next time.

I think that's a issue mr Yamaha should of addressed ages ago, the cush rubbers barely last me 5 minutes.