I've had a few late 90's Cannondale road bikes and they've all been excellent. Some have been abused hard, as in crashed and dented pretty severely, but have yet to encounter a failure or crack of any sort.

I'm a Klein fan too so I've had a few. Two of my road bikes are a 1991 Quantum and a 1995 Quantum II. The latter is a very recent purchase that I've put no miles on yet as it's completely apart for an overhaul (sitting for 15 years) so no review yet. Build quality is high based on initial inspection. The 1991 Quantum has been my primary ride for a couple of years now. Always worked fine and I enjoy the ride despite it being a tad stiffer than a steel frame. The fork steerer recently broke but that has entirely to do with a different stem than original and not being inserted far enough, nothing about the craftsmanship is to blame. Build quality is top notch. I know that's a bit older than you're aiming, just using it as a reference point for build quality.
I did have a 2001 Adept Comp full suspension. Bought it in rough shape, ridden hard and put away wet, but no structural damage to the frame.
Bottom line, I find Klein to be high quality and many who own them feel the same. My two Quantums are definitely forever bikes.

Kleins can fetch a premium but really only the ones with their famous linear fade paint jobs. If you can find one with a more traditional single color paint job, you can get them for about the same as a Cannondale of the same era.