At the 85% cocoa level experience tells us that we should expect a bitter experience. Strangely at this level you can actually get a more intense chocolate than at the 100% level. This paradox often arises due the fact that 100% chocolate makers tend to alter the ratio of cocoa butter to cocoa solids, whereas, this is less frequently the case with 85% dark chocolate.
At this level you tend to witness the true acidity of the cocoa bean in its natural state. Typically you'll still have 15% or so of sugar so there will be a modicum of sweetness, but often it will hardly be noticeable.
It terms of your choices in supermarkets you can get a 'The Best' bar from Morrisons which are very cheap. Lindt do another chocolate at this %. Other options include Green & Blacks, Vivani and the selections below.
Also try some 82% chocolate and compare the differences in flavour notes and intensities.