I think I solved the colour scheme mystery, in the 1990 catalogue you could choose how many colours and how the front fork could be painted, the tricolour Backfire you had and most others I have seen have would have been standard, it looks very much like the original buyer of this bike wanted a Klein but was forced to make concessions in order to be able to afford one, hence the DX. The non 'Elite' Pinnacle of that year came without the mission control bar and stem, so this is definitely a 1990 Pinnacle Elite but unlike the fully loaded model you had mine came with DX and one less colour.
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I'm not going to pretend I've always wanted one or anything like that, but owning and riding a Klein is certainly a box I'd like to tick. I fully expect the experience of riding to be slightly underwhelming, especially after the Fat Chance, I don't think aluminium can ever compete with steel on that front, although my Cannondale is great on roads and light trails, that's mainly because it has very wide tyres and rims plus an extraordinarily long steel stem which all work to cushion smaller bumps, I doubt this will even be able to outdo that.
Looking forward to finding out though and would be happy to be wrong, it wouldn't be the first time.