I have fitted Give Trekker aluminium cases to my XT660X, see http://www.givi.it/Bauletti/Monokey/TRK46N-TREKKER. These are lighter and slightly less wide than the black plastic ones you show above. They cost more but SHOULD last longer. The advantage is that they can be fitted either as pannier or as a topbox, and they have a clever opening mechanism so they can either be opened all the way OR just the top, and you can buy the internal bags so you only need to carry a bag and not the case. The disadvantage is that they cost more of course!! And each case has its own key but they supply spare keys and barrels so you can change them and have a single key for the 2 cases. Clever stuff!!

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(Now sold on, sob) 2011 Blue XT660X with gold wheels, was 26,500 km.
Engine mods: K&N Stage 1 filter, DNA Stage 2 filter, snorkel removed, Kev fuel mod fitted.
Plus: smoked Puig screen, Yam aluminium sump guard, Yamaha / Acerbis handguards, Givi Trekker aluminium side cases, Leo Vince X3 cans plus Kev front fork mod and Fender Xtender. Just fitted Michelin Road Pilot 3 tyres.

SOLD the XTX for a Super Ten 1200. And just bought a Raptor 700 so staying on here for some tips....