Without delving too deeply into the math, it boils down to this.
Without factoring in spelldmg (assuming zero spelldmg, in fact), SoB is always more damaging than SoC. SoC catches up the slower your weapon gets though;
At 2.0 speed, SoB increases your DPS by 35%, SoC by 16.33%
At 3.0 speed, SoB = 35%, SoC = 24.5%
At 4.0 speed, SoB = 35%, SoC = 33%
So as you can see from that trend, with a big slow 2H weapon SoC is *still* the better choice, because Id take a 3% nerf to Seal damage in exchange for that 10% health damage thingy.
SoB's real utility is with 3.0-3.5 speed weapons, it allows you to spank hard without relying on unreliable procs and very, very slow swings.
Unfortunately for SoB, SoC gets a bit of spelldmg and CS is being changed to 6sec (and benefits from both spelldmg and slower weapons) so sadly, Retadins will stick to SoC most likely. It does give Holy Paladins a heavy bat to swing though :).
~sins