The real problem with using other forms like Soresu is that you're using a much weaker form than you should be. By using Soresu specced into Vigilance, you're missing out on all the talents that make Soresu a strong defensive form.
Honestly, you can preach about Guard all you want, but when I really want to Guard someone, I can switch to Soresu on the fly.
I'm also of the opinion that Momentum is incredibly overrated. It's largely a convenience talent because, really, you won't need focus too often after a Leap.
http://www.torhead.com/skill-calc#5000MZIhrkruddMRZhM.1
I just altered my spec slightly for more overall damage and I only had to sacrifice 50% chance in Blade Storm's DoT.