History of 5000 78-95 ???

[bf014@Freenet.HSC.Colorado.EDU (Richard C. Gann)]

I'm considering buying a 5000 series and can't find a brief summary 
of US models from 1978 to the present. 
 
Being a former owner of a Audi 100GL 1978 year model (5000 in US)
I'm also interested in the older models i.e. the big square boxy 
ones pre 1984.
 
I'd like to know what engines were used and models to avoid.
 
I see numerous 5000 CSQ\turbo starting at $5000 and would it be wise 
to get a higher mileage Turbo or go for a straight 2WD 5000 in 
excellent condition or what about a 4000!  
 
I realize that some of these questions are subjective but come guys 
I need some direction!, there just too many dam choices in this country.
 
And while everybody's pondering these deep questions what's the fastest
land animal ????   
 
Thanks 
Richard Gann