Oil gets black and you cannot tell anything by the color (if black). I have done over 12,000 drains on my es and the oil is black. I do not care since the UOA (oil tests) always came back good.
The sludge issue is over blown I feel. I would use whatever oil you want and change every 5,000. Use whatever oil filter you want. If you are testing (and going longer miles), that will tell you about what filter is good, what oil is good/better etc. For that short of time, the oil type does not matter.
For a flush you could use B12 Chemtool, diesel, kero, seafoam, ARX, lc20 etc.