Are the differences primarily cosmetic (e.g. better fit/finish, etc.)? If the Tikka has proven to be just as reliable, tough, dependable, etc. it will be tougher for me to justify spending double.
I researched this a fair amount before my last rifle purchase. Here were my basic conclusions:
Regarding reliability, toughness, dependability, and accuracy... they're equal. Both Tikka's and Sako's have excellent reputations and you won't be disappointed either way on those aspects.
"You get what you pay for"... Although there are cosmetic differences (as expected, more money = better fit/finish), there are also a variety of design differences that you're paying for. To me, the biggest design difference between these is the bolt design, particularly the lug design. The Tikka has a simpler 2-lug bolt while the Sako has a 3-lug bolt. The 3-lug bolt is a bit more complex to machine, so it requires more time/work... for increased cost.
The benefit of a 3-lug design is shorter bolt lift travel: 60 degree 3-lug versus the 90 degree 2-lug. Shorter bolt lift provides greater clearance between the bolt handle and the scope. So, you never have to worry about clearance issues no matter how large your scope is or how low it's mounted.
Also, to me, my perception is that the 3-lug design "feels" faster to cycle. Mechanically, there is a shorter distance that the bolt has to be lifted, so that does kind of makes sense. However... practically, people can also cycle 2-lugs exceptionally fast, so it's not really a significant advantage. I've seen really experienced shooters cycle 2-lugs so fast it's a blur, so I really wouldn't want to try to argue that 3-lugs are faster. That difference of 30 degrees can easily be overcome by shooter practice/skill so there's not really a practical speed difference between the designs.
Thinking of Tikka vs. Sako reminds me of Weatherby Vanguard vs. Mark V. The Vanguard is a cheaper 2-lug design while the Mark V is more expensive with 3 rows of lugs to result in a shorter bolt lift (54 degrees), along with better fit/finish.
Tikka's, Sako's, Vanguard's, and Mark V's all have great reputations for reliability, toughness, dependability, and accuracy for factory rifles. If those are your only concerns, you won't be disappointed with any of them. They all put rounds on target equally well.
If you view your rifle as simply a basic tool to harvest game, then go with a Tikka or Vanguard. It won't let you down and you'll be very happy.
I've also noticed a lot of threads on here with people upgrading, accessorizing, and customizing their Tikka's. If you enjoy doing that, then the Tikka is a great platform to start with, since it's already a great rifle and there are a lot of aftermarket products available for it.
If you want a more refined design and finish out of the box, and don't mind the extra cost up-front, then go with a Sako or Mark V. It will look and feel different in your hands. But... the target won't be able to tell a performance difference.
