What priest spec are you running?
I've tweaked the warlock class to not drain soul so much, and am using an alternative way to cast 'dark soul', since the built-in honorbuddy way will cast it only once then stop. It works, but it spams audible 'spell is not ready' sounds. To turn those off, turn off audible error messages in the WoW client. I'm SO glad I found that setting today!
I've optimized the code more, hopefully that will fix the framerate issue some of you guys have. That's the problem with computer programmers having the latest and greatest computers - we don't always get to see the performance problems some users experience.
I ran it through like 8 battlegrounds, 4 alterac valleys and 4 gilneas. I didn't see it stop, or drop in fps - the fps stayed over 70. It doesn't jerk under heavy load any more (at least on my machine). I also spent lots of time at the training dummy, comparing the dps between FTW and Singular, and it's similar (< 5% difference.) If you're comparing DPS between FTW and Singular, keep this in mind - spending all your cooldowns on the first test, will make the second test suffer by comparison. Test FTW first, then Singular, and see if the numbers reverse.