The 69 gr SMK was designed for a 1-9 twist so I would go as far as to say your T3's 1-8 will stabilize that bullet length fine.
My experience with the 69 SMK was with RE 15 shot in a Savage 1 in 9 twist and was MOA out to 150 yds.
ALLIANT data shows a MAX load of 25.5 grs for 2,956 fps, using Fed. 205 M primers and Winchester, brass. REDUCE THIS LOAD BY 10% and work up ! 2002 data.
It's a HPBT, not an actual varmint bullet, but traveling at that speed they probably make a mess out of any fur and meat they encounter.