You have a 2-stage tac a1 with yodave spring and it's only going 2.5 lbs? That feels odd? Someone else in the Tikka T3 thread mentioned his is adjusted to < 1 lb.
On my T3X CTR, I have it adjusted @ 1lb with the yodave spring.
So either you have a defective trigger, or you installed the yodave spring wrong (maybe put the plunger in backwards?)
On my other Tikka, I ended up having a defective trigger, where it wouldn't go lighter than 2.5 lbs. Some people formulated it was a safety concern and Tikka has started shipping triggers with safety measures, but calling Beretta they said they'd warranty it. Only problem is that I have to send everything back and wait 8-10 days.
So for this long weekend, I purchased the Timney for $180 at redhawkrifles (price shows when you checkout).
I love the 2-stage Timney

But it should perform equally to your Tac A1 if the spring/install etc was working correctly... My Timney is at 8oz 1st stage, and 8 oz 2nd stage (1 lb total pull)