Okay. Here is a mystery that is NOT discussed by the production and magazine reporting public.
Both are NOW coming off basically the same line. Both are NOW basically the same finished rifle.
Here's what's different.
Tikka used to be independent, but were bought and now are a part of the Beretta family since 1988.
If you look, Tikka is more "hunter oriented". Their rifles are more hunter, more lightweight, less mounted sights and less scope mounts, on average.
The Sako is the more tactical, more pre-prepped line. Muzzle breaks,scope mounts, tactical calibers, plus the short throw bolt handle.
Both are cold hammer forged barrels. Many Tikka's are free floated, all the Sako's were that I looked at. Basically they are the same outside of looks.
The Tikka's are pretty; old world wood, the Sako's are more new world polymer/tactical but equally as impressive.
The "custom features" come down to what you want in YOUR rifle.
Hope that helps.