Thought I'd copy-paste my thoughts on Soul Swap from my guild forum and see if there are any errors in this:
Soul Swap is a case of Soul Swap damage + 1 gained GCD every 24 seconds versus lost BoA damage, since you spend 2 GCDS fully refreshing all DOTs on the off-target where you would otherwise have spent 3. Looking at the top Aff log available for Valiona & Theralion:
World of Logs - Real Time Raid Analysis
'Soul Swap' does an average of 4.26K damage
'Soul Swap Exhale' does an average of 3.75K damage
Since each GCD gained could be spent on better uptime of DOTs on the main target, keeping Shadow Embrace or Haunt up, Drain Soul etc. we can only assume each GCD is worth 28.5K damage (since he's doing 28.5K DPS)
That's a total of 36.5K damage gained.
Soul Swap is used in an ideal situation roughly every 18 seconds (duration of Corruption) and absolutely can be used without clipping either UA or Corruption, meaning that BoA will only tick for 18 seconds so you are losing 6 seconds of its highest damage.
Now calculating BoA's damage is a bit more messy and I'm not sure how to do it 100% accurately, but if you assume it ticks roughly every 1.5 seconds (and that's assuming a lot of Haste) then it will tick 4 times in that space of time.
4 ticks of BoA vs 36.5 K damage = BoA would have to tick for ~9K damage each time. BoA never ticks/crits for that much, not even close.
Even though these are rough figures I think the maths swings so far is Soul Swaps favour that I have a hard time seeing why it
wouldn't be worth it.