I think 20 and 1:8 twist for the bullet weights you plan to use is fine.
But...if it were me...I would choose a stiff, high quality 16.5" barrel with a threaded muzzle (for a linear comp) and a 1:7 twist to handle heavier bullets should you choose to use them at some point. Especially if you are planning on shooting under 300 yards most or nearly all the time, which it sounds like you are.
There's still plenty of velocity and energy with that barrel length. No it's not "efficient" nor the proscribed "optimal" length for the round, but IMO the benefits outweigh protocol. The new SiG Cross doesn't come in 7-08, but if you aren't wed to the round, you can get one in 6.5cm (18" brl) or 308 (16" brl) - and I'd suggest just buying it and be done. [No, I do not work for Sig nor have any financial interest in the firm - I just like to recognize good design, and the Cross scratches my itch (light weight, short barrel, folding stock).]
I had a custom rifle with a 18" 308 and a 1:10 twist, with an AI folding stock, and shot Lapua Scenar 155gr ammo in it. Supersonic past 1000 yards even with that "short" barrel. Plenty good enough for all NA medium game and even longer range mountain shots.
As always, choose the right optic, ensure proper shot placement and practice, practice, practice.