I doubt you will quantify the difference between a 1:8 and a 1:7. Both will stabilize an 80gr pill just fine, which is all you need for long range F-class type work, which just makes hitting the X ring just than fraction easier, particularly under blustery condition. BTW just remember running those fancy "VLD" type pills is expensive and probably won't feed from the mag at optimal length - single load only. Me, I'm more a humble 69gr SMK man
Don't prioritize twist as a requirement - just take what you can get, a 1:8 will do fine.
With regard to barrel, there's only so far a factory barrel will take you; if you want to be competitive, you should be looking at aftermarket options, like a Krieger or Bartlein or Benchmark (or any "match" grade aftermarket barrel will probably do). Second to the barrel is the action; as mentioned by SCJ, the Barnard is the comp standard, but you can still build a laser on a cheaper action like the tikka or remington or perhaps howa, if you are on a budget.
Personally, I'd be looking at a custom build off the bat. You can have a custom built rifle made on a moderate donar for less than the cost of those fancy tactical things, that will likely shoot better.
I've just had a custom crossover TR/light-F built myself which was a KRG BRAVO stock + tikka t3 donar action + 30cal Krieger Palma, for less than $3000. It runs a 10-shot mag and it'll shoot Xs out to 800m, if you're doing your bit.
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I've also built a 223 on an old HOWA donar, with a Lothar-Walther 1:9 - that thing's also a god-damned laser, but more a 500m gun.
In2.