Been making fennekin babies. Got one with no evs, modest, "outstanding" IVs and 31 HP, 31 spe, and it seems 28 SpA
Fennekin level 19 stats:
50/23/24/36/31/33
Level 50 flat battle stats:
115/54/55/89/75/80
Braixen level 20 stats:
59/29/32/50/37/40
Level 50 flat battle stats:
134/67/73/119/85/93
Delphox level 36 stats:
111/55/64/106/84/91
waiting on someone to accept a battle so i can get the level 50 stats for Delphox but looks like it has base 75 hp, 115 spa, 105 speed
How do you know the SpA IV? Doesn't it just give a range of 26-30? Otherwise, this supports my claim of 40/45/40/61/60/60 base for Fennekin...that being said, jumping from 81(neutral) to 109 SPATK indicates a growth of 28 base to Braixen, which I can support on evolving on 16 and growing 9. Interestingly enough, that puts her 61-62 base up to 89-90. But, my brother's Braixen -> Delphox evolution was only 17 on 36, indicating somewhere between 23 and 24 base since it cannot hit 25. That would place Delphox's SPATK base between 112 and 114 instead of 115.
Furthermore, IF the speed is perfect, it is easy to see that Fennekin's should be 80.5, thusly 93.5 for Braixen. Scaled to level 36, Braixen's would've been 68.72. Growing to 91 is a difference of 22.28-23.27. 21.6 is 60% of level, 22.32 is a base increase of 31, but the range in general scaled to 50 is 30.944-32.319 meaning it is either going to be 31 or 32. That will land the speed at either 104 or 105. Meanwhile, with max HP, scaled Braixen has 99.64. This produces only an increase of 11.36-12.35. Scaled range is 15.777-17.15, so this one could hit a few bases. Since fennekin starts with 40 base and grows 19, I would agree that 16 seems the most likely, ending up at 75.
The defense seems to grow in the exact same manner...except it only grew 36 in the first stage. Braixen's defense there is either 73.0 or 73.5. Scaled to 36, it is 53.96 or 54.32. Range could be 13-15. This means the bonus from Fennekin to Delphox is 31-33. That would put the base at 71-73.
The same can be done for other stats, but I find it difficult to do with attack because that level 50 Braixen could be 61 or 60 un-personality in attack.
Still, by rough estimate of the attack stat, I would say this looks like 75/70/72/113/100/105 as Delphox base for a total of 535. Attack from Braixen to Delphox is clearly an increase of base 10 with 15 as a potential growth from the first stager.