I have OCD about not using lower GS weapons, so I also have an LVOA-C with Destructive and a marksman (a Police Mk17, but whatever preference works) with Coolheaded in the free slot, to adapt to whatever focus I need. I rarely use the marksman, but it can be helpful in group play to help skill spamming a bit (that internal cooldown really limits it) Although I can get kills fairly consistently with the Determined M4 and the M4 builds the stacks better--by the time a solid stack is built, skills are often back anyway under real world practice.
I prefer the 5-piece and Barrett's over something with Inventive as I prefer the higher stats and 5-piece bonus. Personally, I can more guarantee having both skills off cooldown more than I can rely on being at full health, since I run the faster recharge skills--if I ran a turret or something, this would likely change. With everything off cooldown, 14 stacks tops the skill power soft cap. With the fire rate and steadiness of the M4 variants, I can hit that pretty quickly. Another fast 10 stacks and it compensates for the 10% from Barrett's when skills are on cooldown (plus an extra 5% damage at that point, too). Getting a Talented weapon kill proc is gravy (definitely not something to rely on, though, but there aren't many options if you don't want to drop to a lower GS tier). You can't double-fire your skills for their maximum damage like with an Inventive pack, but you can keep up a pretty consistent skill usage by interspersing weapon fire. If something NEEDS to die, it's literally seconds until I've got the 10% Barrett's bonus from any given time. Possibly, a 30 stack with 1 cooldown and the 5% damage may give better results due to the soft cap but I've never done that math (cooldowns always run out too fast when I jump into the menu to check). It's probably a close enough wash to not worry one way or the other under stress.
I like a little bit of Health on Kill in some capacity, even for group PVE, but the 5% on gloves could be swapped for a different preference. I think it helps give an extra boost when I need it, especially when running my Sustained/Predatory M4. Also, my mods are not fully optimized (I probably wouldn't bother with Range on any if given the choice, obviously), but the numbers are small enough I don't think any of those stats make or break it.
Also, stats seem wrong, even with about 19 SP missing from unoptimized mods, putting my Electronics at 9057. I'm not sure it's picking up the 5-piece Tac bonus, as I have 45% skill haste instead of the listed 40%. Firearms and Stam numbers are right, although my Firepower is a fair amount lower and Toughness is about 1k less than listed. It also must be showing my skill power without Barrett's bonus as it's normally at 404.5k.