Go 1:8 unless you want to shoot the >69gr at longer ranges past say 600 yards in which case look 1:7.
It'll still shoot lighter bullets without any problems unless you want to shoot 40gr varmint grenades.
There is a 2nd hand Tikka in sales. But you can't see sales till you've been on here a while and posted on a few threads. Its been up for sale for over a week so will probably be there in another.
I still don't understand why Tikka/Sako produce 1:8 as specials unless its aimed at the conservative shooter who has always shot 1:12 and will continue to shoot 1:12.