The short answer:
Pocketed mods (standard or Deep) always out-perform Light or Ultra-Light builds in terms of their net increase to your available Carry Capacity.
However, it is worth noting that the Light and Ultra-Light builds have bonuses and side-effects other than just freeing up Carry Capacity. Particularly, they improve stealth due to the lower total weight in worn Armor and they come with AP Cap boosts.
The long answer:
The boosts that you'll see from these mods is different, depending on the type of armor and the armor slot. The weight of the mods also varies by armor type and slot. So, if you're looking to mix mods within your suit of armor, you'll want to take this into consideration in order to optimize the results according to your play style.
Nukapedia's Fallout 4 Armor Mods page does not yet have complete data on mods across all armor types/slots. However, if patterns for Leather Armor mods hold true across all other armor types, we can assume the following:
- Within an armor type, Pocketed/Deep Pocketed mods provide the same boost no matter what piece of armor they're used on. (e.g.: You get +10 Carry Capacity from Deep Pocketed armor when applied to Leather Armor, regardless of whether it's on the Chest, Arms, or Legs.)
- Within an armor type, the absolute value of a modifier's weight will be less on Non-Chest pieces. (This provides a small boost to the net gain in Carry Capacity from Pocketed/Deep Pocketed, but substantially reduces the weight-reduction value of Light/Ultra-Light.)
- Light/Ultra-Light AP boosts are substantially less (looks like half, rounded down) on Non-Chest pieces.
Given this, if you want to mix modifiers so that you can have an AP boost while still getting substantial gains in your available Carry Capacity, the choice is fairly simple. Put Light/Ultra-Light on your chest piece, and Pocketed/Deep Pocketed on everything else.
That said, as a case example, here's exactly how much a full set of Deep Pocketed Leather Armor will out-perform Ultra-Light Leather Armor in terms of Carry Capacity increase.
Deep Pocketed Leather
- CC boost: 10
- Weight: .5
- Net Gain: 9.5
- CC boost: 10
- Weight: .2
- Net Gain: 9.8
Total Net Carry Capacity Gain (Chest + (Non-Chest * 4)): 48.7
- Chest Weight: -4
- Non-Chest Weight: -1.7
Total Weight Reduction (Chest + (Non-Chest * 4)): 10.8
Essentially, in terms of freeing up room in your Carry Capacity, a full set of Ultra-Light armor can only out-perform a single piece of Deep Pocketed armor - even then, only by a little bit. And it can even still be beat out by only three pieces of Pocketed armor (each having a boost of at least +5, and weighing relatively little in comparison to that boost).
About Stat Boosts for Armorer
Skill Points needed to unlock the various Armorer perks are, in a certain respect, inconsequential to this discussion. All Armorer levels require the same SPECIAL stat level to unlock, with the only other difference in requirement being in overall character level.
That said, currently the highest boost (not counting mod weight) you can get from Deep Pocketed is +20 per piece. To match that boost with your SPECIAL alone would require +10 Strength (+10 Carry Capacity per Strength). If you invest in Strong Back (+50 at level 2), you can reduce the points expenditure to 7.
Armorer 4 requires a character level of 39, but Strong Back 4 only needs level 30. So, anyone who starts with a Strength of 5 or less can get a boost in Carry Capacity, equivalent to a full set of the best Deep Pocketed armor, through SPECIAL and perks by level 30.
(Note: I haven't yet looked into whether Deep Pocketed actually needs Armorer 4, or needs it for all armor types, so it's possible the equivalent boost may be achievable earlier and by characters with a higher starting Strength. If Deep Pocketed is available for all armor types with Armorer 3 or less, then the cost/benefit in terms of skill points per Carry Capacity for each would change substantially.)