One of the things that's always bugged me about GURPS is the difference between point shooting and aiming. Having tracked down a copy of Tactical Shooting to peruse, the approximation of quick aiming (taught by all the various shooting schools and videos, like Magpul's art of the dynamic tactical combat whatever) is sighted aiming, at +1.
I think what I'll do is offer Quick Aim as a specialized perk for those with a skill of 14 or better in a particular gun skill, switching the effect of All-Out Attack (determined) to functioning as the Gunslinger perk, rather than just a +1.
With at least one point in the Quick Aim perk and at least one gun skill at 16 or better, the price of Gunslinger drops to 10 points. While the books say Gunslinger is supposed to be cinematic, it's actually pretty easy to train, and most modern combat shooting schools do a lot for training such that when you point your gun the sights align properly. Might not be as good as taking time to aim proper, but it makes combat at medium ranges DRASTICALLY more feasible than the standard rules for GURPS allows.