'86 4ks power drop off

[enzeder@ix.netcom.com]

G'day Folks,

Two questions:

1: My '86 4ks is losing power (bogging down), and the speed at which the car bogs down is getting lower.  Started at about 60mph once last week and then 
seemed ok, then this week droped down to 40mph while I was on I-95.  I pulled over to check vacuum hoses and electrical connectors and all seemed ok.  
Got back in and drove off again at about 60mph, but by the time I got into town I could barely hold 40mph again.  At least it got me home.  I have a 
Bentley manual and went through the trouble shooting tree for the ignition (hall sender, coil, dist., etc) and all checked out ok.  I didn't touch the 
knock sensor because the manual says to be exacting on the torque of the bolt and I don't have a torque wrench.  Is there a way to test the knock sensor?  
Can the knock sensor be this disruptive?  If it matters, the car starts and idles perfectly.  Also, it has a little over 200k miles and until last week 
was doing great.  It has the 1.8L/auto.

2: The car needs other work, but I don't want to do a rolling restoration so I'm about to buy another used Audi to keep me mobile.  The three cars in the 
area that interest me are: 
86 4kcsq ~ 150k ~$3k
86 5ktq  ~ 150k ~$3k
87 5kq   ~ 120k ~$4k has ABS
All three are stick shift and I've listed them in order of my preference.  I put the 4k on top because it seems to have been well maintained.  I'm 
curious about things like how much extra weight the 5k has to haul around (although I guess the turbo would more than make up for that), what to look for 
on the turbo, opinions, etc.

Thanks,

Arryn.