It's been a few days, and I decided to switch my STF from 18/21 with ~50 body armor to 15/24 65 body armor. Weight was increased by 10, which simulates an increase of 5 weight in armor and a 5 weight shield to compare what my main will be using, increasing from 55 body armor to 64 body armor. Even with 2IF and 15 strength, 54Hp, I was tanking quite a few hits. The 8ath allowed me high levels of control, even with higher armor. I feel 7ath and high armor might not be as fast as I want, since I want to be comparatively faster than my opponent, not the same/less speed, although I still haven't tested that yet.
It was safe to say that my performance more than doubled. My 18/21 with medium/low body armor had a KD of 2.5:1, and after the last 5 maps, my 15:24 with high armor had 5.8:1. The higher weight didn't change the great amount of acceleration I had. Being able to manipulate speed bonus on myself with high armor really helped mitigate a lot of damage. 21/24 on my main is looking quite great now, despite the low Hp, although I would only be able to increase shield skill to 6 at most.
Right now, 21/24 > 24/21 >>> 21/21. 2 Shield skill + 7-11 Hp doesn't compete with avoiding more attacks and killing enemies with less swings. Since shield skill doesn't affect melee forcefield, higher ath allows me to catch archers, and higher armor reduces arrow damage if I do get shot in a blind spot. Of course, 21/21 is the most future-proof if any changes occur to IF and shield. So in the end, kudos to Matey and Rustyspoon in the agi shielder lobby.