The only variable is the pre-boil volume. At 5.5 gal, it'll be ~66% efficiency. At 7.5 gal, it's ~76%. Since you aren't compounding it with a second batch, the range is really pretty small.

Just still not following, why would a 5.5 gallon batch of 1.075 have a 66% efficiency and a 7.5 gallon batch a 76% efficiency. Are you assuming using the same amount of grist or something and just adding more and more water?

Those are both assuming 5 gal at 1.075 post-boil. The grist quantity changes when the efficiency changes - more boiloff means greater efficiency.

16.0 lb grist, 7.4 gal strike -> 5.5 gal of 1.068 wort (66% eff.)

13.5 lb grist, 9.1 gal strike -> 7.5 gal of 1.049 wort (76% eff.)

Somebody help me wrap my brain around all the stats for a 1.075 - 5 gallon finished batch size on a NO-SPARGE (meaning only drain the tun) which would have a 75% efficiency.

Most likely, you wouldn't want to get 75% efficiency on a 1.075 beer since it would require boiling off 1/3 of the pre-boil volume. With a more typical pre-boil volume (6.5 gal), the efficiency would be ~71%.