This is something a bunch of us were talking about last night at Nirvana Coffee.
Mark found best results with the Mexican decafe when he roasted it a lot light than he would with the swiss water decafes. And i agree. Once you go to that oily stage in a decafes life it greatly reduces its shelf life, id say by half that of normal coffee.
I tried some of his mexican last night with a color of about CS 8 and it was quite enjoyable.
If you want to blend it with something else for a halfcafe of sorts try something that will compliment it.
I would strongly suggest find who stocks the Brazilian Daterra Opus 1 Exotic in Australia as it is a natural 1% caffeine veriety of coffee.