-Speedloader should be at no priority -- it only applies to normal shots.
-Gun Booster increases damage directly and should be at high priorty. No it's not a typo, it has always been 20 AC. If you read the skill, it increases Gun AP by 400, which when translated to AC is 20 AC.
-Compound Mastery should be no priority. According to numerous tests, it doesn't visibly work.
-Shooting Spree is probably one of the better (I personally think it's top 5 at the least) AoE's in the game. Don't you dare disgrace it.
-99% is an incorrect statistic. Once you get to bossing or just higher leveled monsters in general, you actually need LK. I think the second-to-last (the Eye) CT boss needs some 300 LK. Which, if you're unfunded, makes for an interesting challenge.