All bikes are not created equal. All folders are not created equal. A bike, folding or non-folding, built to go fast or far will, with a reasonably prepared pilot, go fast or far with no issues. A bike built solely to get small may or may not be particularly good at going fast or far. Anyone reading Jur's posts knows that he has spent countless hours sweating over the details of his bikes. It shouldn't be a surprise that those bikes are as comfortable as anything else he's going to ride.
I bought my way out of the problem by getting a Bike Friday. They are built to fit and ride like a full size bike. There is some difference in the feel of the bike from a full size bike, but there is no problem with discomfort or, that I can tell, any substantial loss in performance.
Speedo