Stacking calculator here.The long-and-short of it is:
3 complex damage mods: Individual bonuses: 5.00%, 4.35%, 2.85%, Total bonus: 12.69%
4 complex damage mods: Individual bonuses: 5.00%, 4.35%, 2.85%, 1.41%, Total bonus: 14.28%
This.And does anyone actually expect a cloak to help them snipe? You do know that it's deactivated when you swap to a weapon, right? You do know that the smallest cool off is 30 seconds, right? So, are you all suggesting that you're going to wait at least 30 second between shots? I'm betting that cloaks are going to be a let down in general, and I am certain they will not increase the viability of sniping in 1.8.
After reviewing the dropsuit charts, I am almost certain that for sniping, I'll stick to the Amarr logi suit. Its 3 high slots will grant a 12.69% damage bonus with 3 complex damage mods, with another 15% from SR proficiency 5, for a total damage output increase of about 29.60% (eg, base damage = 100 * 1.1269 = 112.69 * 1.15 = 129.60). For comparison, 4 complex damage mods (possible with the Caldari and Minmatar logi frames) gives you an increase of 31.42% (eg, base damage = 100 * 1.1428 = 114.28 * 1.15 = 131.422; the 5th mod would only add another .53%, ie, it's pretty worthless).
Here's some math for shields vs. armor, using a charge SR:
Amarr logi, 3 complex damage modsBase damage = 321.9
Shields math: 321.9 * 1.296* .9 (90% vs shields) = 375.46 * 1.75 (headshot bonus) = 657.1
Armor math: 321.9 * 1.296 * 1.1 (110% vs armor) = 458.9 * 1.75 (headshot bonus) = 803.08
So, you can expect to do between 375 and 459 body damage, between 657 and 803 headshot damage, with this setup.
Caldari/Minnie logi, 4 complex damage modsBase damage = 321.9
Shields math: 321.9 * 1.31422 * .9 (90% vs shields) = 380.74 * 1.75 (headshot bonus) = 666.30
Armor math: 321.9 * 1.31422 * 1.1 (110% vs armor) = 465.35 * 1.75 (headshot bonus) = 814.37
You can expect to do between 381 and 465 body damage, between 666 and 814 headshot damage, with this one.
IMO, the approximately 1.5% damage output increase between the 3 complex damage mods vs 4 is not worth the loss of a sidearm. For this reason, I think the Amarr logi suit will continue to be the best suit for sniping. With an advanced+ armor repper and three complex plates, this suit tanks over 800 EHP, has a sidearm, grenades, and three equipment slots. The only thing it can't tank are charge/Thales headshots from a maxed out Caldari commando sniper stacking damage mods, and a direct hit from an FG (but that's true of 95% of fittings anyway).
I'll take extra equipment and grenades over the slow, explosive-less commando suit any day.