Given good conditions, amazon swords tend to get ridiculous. I've seen comedically large swords in 10g, 20L, etc. I would say that a happy sword could easily get 20", but I wouldn't dare try to peg the maximum limit lest it take it as a challenge.
Microsword is more demanding than most plants, as are most foreground, especially considering most people are looking for a 'carpeting' effect. That being said, it's a slower grower and more tolerant of less than ideal setups than other foregrounds like HC or DHG, so it's a good 'gateway' foreground assuming you're willing to meet it halfway.