Way to go Lukemac!
Great that you are seeing self-application and concentration.
Lots of kids, even with those extra 5 points to cross the DYS line find Kindy kind of fun, especially if it's half day.
Awesome on the retest discount - LOL on testing at 6y3month - now I get it that this shows your son to his 'best advantage.'
Personally - I'd rather test at 6y1.5months to get the 'most accurate read possible' than goose it to get the 'most likely to cross DYS line' scores. But that's because messing with my head is so easy to do - I like to keep my feet on the ground as much as possible. Of course, if you think that everyone else is waiting until 6.3, then keep the plan - you don't want to shoot yourself in the foot over the 'SUV problem.'
The problem is that if you knowingly goose the scores, you may end up spending tons more money than you would need too under more acurate circumstances.
Of course, depending on how good the child is a 'self-differentiation' - and some kids are excellent as 'squeezing every drop' out of an assignment (different than aiming for perfection in a dangerous way) by adding creativity to the mix - if the current scores are accurate then your child - and depending you the demographics of your local schools - you child might be fitting right in at the public school or a total fish out of water - personality matters.
Read up on Sylvia Rimm's parenting books and get ready to 'ask you son for more' academically. One boy we know had a family rule that if the teacher asked for one paragraph, he had to write 2. If the teacher asked for 6 pages, he had to write 12. That kid was much more gifted than my son, but didn't need the gradeskip because he was getting excellent parenting.
Best Wishes,
Grinity