Single or Dual voice coil?

Yor optionas would be,

1. SVC brige 2 channels for 400w on the sub and have two channels free- mabey for components?

2. DVC bridge two channels together, take the two briged outputs and drive both channels of the sub (why?).

3. Run the DVC sub with two channels and leave two for components, etc.

What are you trying to do exactly?  What equipment are you looking at?

I think, if I understand your question right, that you believe that a woofer with dual voice coils would need two hookups to an amp.  Not the case, as DVC woofers are available to supply us with an endless array of configuration possibilities, depending on what the coils are and how many we use.  In your case, you want to use one sub.  The total of the coils impedence have to match your amplifier rating.  If you want to use one amp to power the front components and a sub, a four channel amp will work.  The sub should be either a single coil 4 ohm, or a dual coil 2 ohm.  See this wizard for the different wiring configurations using DVC subs.  The RMS rating of the sub has nothing to do with the number of coils, and should closely match the amplifier power at its bridged rating.  So wire the components to channels one and two, and bridge the sub to channels three and four.

Otherwise, if I read your question another way, you want to know if wiring two coils to separate channels is better than bridging?  No.  Wire the coils together on the sub, then bridge to the amp.

I am presuming you meant a 50 X 4 amp, total of 200 watts @ 4 ohm.  If you are talking 800 watts at 4 ohm, though, like your post indicates...there are some other better solutions.  In that case, post up what you are looking at and what you want to achieve.