A lot of the good animal companions get large at 7th level. How does this interact with the large evolution? Since the bonuses are the same my gut is that the 4 point version isn't applicable, but that you can eventually spend to spend 6 points to up size to huge, based on the extra text.
If 6 additional evolution points are spent, the eidolon instead becomes Huge. The eidolon gains a +16 bonus to Strength, a +8 bonus to Constitution, and a +5 bonus to its natural armor. It takes a –4 penalty to its Dexterity. This size change also give the creature a –2 size penalty to its AC and attack rolls, a +2 bonus to its CMB and CMD, 10-foot reach, a –4 penalty on Fly skill checks, and a –8 penalty on Stealth skill checks. If the eidolon has the biped base form, its reach increases to 15 feet (10 feet for all other base forms). Any reach evolutions the eidolon possesses are added to this total. These bonuses and penalties replace, and do not stack with, those gained from becoming Large. The summoner must be at least 13th level before selecting this option.
The ability increase evolution costs twice as much (4 evolution points) when adding to the Strength or Constitution scores of a Large or Huge eidolon.
Does that make sense? I couldn't find an official ruling and I just wanted to see what other people think. I think given the level prereq and spending 6 points is enough, any thoughts?
I suppose if you wait till lvl 13 it would be fine.