No matter what gauge flats you try, they will feel more 'tense'. Tension is the wrong word for this topic - flexibility is more accurate. Because the way a flatwound is contstructed, bends are harder to do. Hence, people perceive this has more tension. Rounds and flats are very close tension wise (in similar gauges). Flats are harder to bend than rounds. Other than that, smoother, less finger noise and all the other great qualities of flats to boot.