Pinnacle = basic model with rack/fender mounts, 1" headtube
Rascal / Top Gun = evolution of Pinnacle, no fender mounts, more racy geometry, 1" headtube. Used single butted and plain gauge tubing.
Fervor = essentially same frame as Rascal
Pulse 94-95/Pulse II 96 = Rascal successor, first Klein frame to use 1 1/8" headtube. Came only with suspension fork and therefore the geometry was developed as suspension ready. Used light Gradient tubing and was the lightest Klein frame available.
Attitude 90-92 = Same as Rascal but used Klein Precision 2" headset and Uniklein forks. The 90-91 models came with welded boxy crown.
Attitude 93 = Downtube went from to 42mm to 48mm and seattube went from 31.8mm to 34.9mm (using 27.2mm and 31.6mm seatpost respectively). More butted tubes --> lighter weight.
Attitude 94-96 = New MC2 frame, used Gradient tubing, about 1 lbs lighter than the MC1 frame. Used new "aheadset-like" fork & stem system. The headset used 2" lower and 1.75" upper bearings.
Adroit 91-93 = Top model, used 50mm (2") downtube. First 91 models had 31.8mm seattube and boxy crowned fork but these are very rare. Most Adroits came with 34.9mm seattube. These Adroits had double & triple butted tubing (rear stays were single butted). The fork and seat & chain stays were reinforced with boron/carbon fiber and the rear dropouts were drilled for weight savings. Some paintjobs were Adroit exclusives.
Adroit 94-96 = New MC2 frame, same as Attitude with the exception of 2" downtube. Didn't have boron/carbon anymore, except on the fork. Weight essentially same with Attitude whereas the old Adroit was 1/2 lbs lighter than Attitude.
Adroit 96 = With the exception of the very first 96 Adroits, most of them were actually Attitudes with Adroit paintjobs and stickers. So, even if there might be X in the serial #, the downtube can be Attitude's 48mm.
Adept = Rare hybrid with only a handful made during 1992-95. Essentially an Adroit with 700C tyres and no boron/carbon. Frameset was lighter than Attitude thanks to double & triple butted tubing.
I don't get deep into the race bikes but essentially:
Quantum = base model
Quantum II = lighter, cables inside the frame
Quantum Pro = used MC2 headtube, Aeros fork, etc.
Aeolus = 650C triathlon frame
Panache / Kirstin = small frame for ladies
Performance = touring bike
There were also Team Super, Stage and Custom frame available. The Klein catalogue said that the Team Super was the best frame Klein could produce. It had boron/carbon layers just like Adroit.
Carsten can give you more specific info but I hope this helps at least a bit.