Looking to build my second ar pistol, this one with a brace. I have two questions. 1) What buffer/spring do y'all reccomend with a 11.5 upper? 2) Any idea if the sb pdw will be longer than the new 13.5" "requirement"?

I would at least run an H buffer...standard spring is good but go with either Damage Industries or Sprinco for long life.

I enjoy my PDW brace...a lot...at full extension it has 9.25" LOP.

The PDW does not extend out past 13.5''.

Buffer and spring weight is dependent on the particular gun and how you intend to use it. The gas, carrier, load and friction will determine how fast the carrier cycles and what spring/buffer is ideal. Until the AR is tested it's hard to say what will work best.  
I use a standard weight spring and a carbine weight buffer in most cases. If you want the highest reliability, it's better to have a strong cycle that allows the buffer to just tap the rear of the buffer tube. In most cases a carbine buffer accomplishes this. In some cases a heavier buffer is needed to accomplishes this. An over functioning AR that beats the buffer against the rear of the buffer tube is not as reliable, IMO.
If you want a slower and possibly softer cycle, a heavier buffer can be used to stop the buffer from reaching the rear of the tube but still allow the gun to function under consistent conditions. Deliberately upping the buffer weight so that an AR barely cycles is not as reliable, IMO.
Upping spring weight is generally a bad idea unless your fighting gas problems. The heavier the spring weight becomes the less forgiving the AR will be to temperature and load changes.  In some cases of over function a heavier spring makes sense though.

Thank yall for your replies. I'll be going sprinco blue/H buffer (unless you think I should go diff). Now on the hunt for a fde pdw brace.  Thanks again!