Based on what you have stated, the best options from Motiv would be either the Tribal or the Ascent Apex.  However, I don't know if I would consider those skid/flip.  The Tribal is a bit stronger than the Ascent Apex but might be too much when the lanes are truly dry.  The Ascent Apex is better for those conditions based on your stats.  However, for the heavier handed or slower bowler, the original Ascent would be better for desert conditions.  It has an older and weaker cover.

For replacing the Yeti, I would figure the Octane would be the best option with the Primal Rage being a little stronger, though not as skid/flip as you say.  The cover on the Octane is quicker reacting.  (as long as you are looking for skid/flip)

For a league arsenal, the Tribal and Apex are probably similar enough to not warrant both.  However, the original Ascent is a decent step below the Tribal.

If you are a stroker, then I am not sure if you would need much below the Apex if it was your ball below the Octane.  If you wanted to cover more conditions, then a Sinister - Octane - Tribal - original Ascent will cover 99% of what you should see. 

The Sinister comes at 4000 grit.  Not sure how they apply that 4000 grit, but if it is like Storm, then perhaps it is on top of 1000 grit. 

You could start back at 1000 and work your way up using 2000 then 4000.  When I follow this method, I get a shinier looking ball than what Storm or Roto Grip get when they say 4000. 

I personally use polish as a last resort.  I have a harder time reproducing polished results as opposed to abralon results.

I would have a pin-to-pap length around the 4.5-5-inch range and adjust the cover to get the length you are looking for.