I'm 5'6.5 and I ride my first gen KLR with no problems, but I've been riding for 30+ years. I'm used to it.
In My area KLR's come up for sale a lot and you can get a nicely kitted one in the price ranges that you listed for both bikes.
The 1991 is pretty old in my opinion, but if it's been well maintained it could be okay.
It's always so hard to say what something is really worth when dealing with used bikes.
In the end it's probably going to just be a gut decision.