Okay, actual performance thoughts: First, is the engine stock? If so...run stock plugs. While I may ignore stock rec's on, say, a TBI SBC (with HEI! mmm acronyms) or other more primitive engines of the same vintage (including non-stock gapping), I generally leave ze Germans alone.
There may be some widespread agreement that something else works better for your Bimmer- but I am not a BMW enthusiast and as such would try stock replacements by default. Though I do avoid Bosch plugs, which are the OEM brand on some (most?) German cars.
You really can't read those plugs. They're just too destroyed to look for proper heat range or fuel mixture. I guess you can read general combustion efficiency (...poor), but that's obviously skewed by the poor operation of the plugs. I would have a strong suspicion that they are too hot (need a lower heat range plug), but wouldn't exactly be betting money on it. You're getting detonation/preignition, though. That can be attributed to heat range, but I doubt it's the only cause here.
I have rarely if ever used the ubiquitous 'spark plug condition' chart, as 99% of the plugs I remove either look fine, or have pretty typical problems like worn electrodes or oil fouling...for yours, I took a glance at it to remember what it called that crusty crap on cylinder 5.
Ash deposits, apparently. I'll let someone else who's maybe seen that more weigh in on the cause of that, 'cause I'm frankly not sure. I would guess maybe the valve seals are dry and hard and one on that cylinder has just cracked apart and ceased to be.
Cylinder 2 is the closest to looking like a normal (albeit in need of replacement) plug.
your engine actually ran with those plugs? On all cylinders?
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