To compare displayed called shot odds with beta 2:
Take ArcLight from the PDX Combat Basics stream last week. Her stats and abilities haven't changed, the passive perks from the skill points have, but we don't have a full list of the Tactics tree yet, so that's as close as we can get to comparisons.
Called Shots on fallen target w/ 80% PPC and 75% LRM base hit %.
Head 3% from 12% in Beta 2
CT 54% from 69%
LT/RT 38% from 60%
Arm/Leg 23% from 47%
Witness, who has a higher Gunnery than ArcLight (4Gun, 6Tac vs 3Gun, 8Tac) in the stream gets a 60% on the CT. I'd imagine someone like Kraken with 5Gun, 6Tac would be best for reliable called shots.
Keep in mind, there were a lot of small UI bugs with called shots and it was found that the real results didn't match the odds shown due to how they calculate those numbers. Until we get our hands on the game, we only have the displayed values to compare, but it seems we won't be reliably coring out CTs with massed SRM/ML fire as easily as it was in beta.