   Drawing order
  Hey I have a reasonably simple question this time. If I have sorted polygons into groups using the same material and then separated the solid from the transparent ones would simple sorting each group of polygons front to back/back to front be sufficient rather than sorting each polygon individually. I'm more concerned about problems displaying transparent polygons rather than missing out on the early Z test thing.   
  You really want to avoid per-frame sorting at polygon level. For solid objects, the Z buffer handles all visibility problems. For transparent objects, you should create them so that sorting back-to-front on object level avoids artifacts. Big, concavelike objects might cause issues with alpha blending. They should be broken into smaller ones as a preprocessing step and sorting should be done on these subobjects, not at single polygon level.It really depends whether solids objects should be sorted front-to-back. If you're GPU-bound (moreover, fillrate or shading performance -bound), it will help. If you're CPU-bound already, sorting solids will only increase CPU's load.You really want to profile this for yourself to see which is more convenient.