TL:DR - 4 Crisis isn't cost beneficial in almost any situation, but 4 Stealth can make a HUGE durability difference depending on your style of play.
Even when using CIBs, I don't run bigger crisis teams because of the temptation to make the drone squads too large. Anything more than 6 Drones (actually 4) becomes highly susceptible to morale itself. If I have enough points left over to throw another crisis suit in then I'll generally go for a BC Hazard w/ATS. For the points, he is way more durable with a much higher output when used to target the right units and can bring in 4 drones.
I generally go for 2 Dual purpose 3-man CIB squads, 1 anti-infantry 3-man Flamer Bodyguard squad, and if I have the points left over, throw in a Hazard with 4 drones. Also keep in mind, if you can shave another 50 or so points off, you can just throw in another QFC instead, making a 4th crisis suit almost always the worst option.
All of that being said, I often use Stealth Teams with a homing beacon to bring in my Flamer suits or QFCs, so if I know I'm going against a hard hitting alpha strike list, there can be a benefit to using those extra points to beef up your Stealth Teams to ensure you can get off a Manta Strike response.
In my most recent game, my opponent was using two Wraith Knights with Farseer support along with that Super OP 1CP Fire Prism formation that allows you to ignore LoS, range, double tap for 2D6 S6 AP-3 shots, AND reroll all failed hits and wounds. I had first turn, but he seized. Fortunately I had used some points to beef up my stealth teams with an extra member with a SG in each of the 3 teams. His Knights were on me first turn in CC with 12 attacks each and he webwayed 10 Wrathguard with their ridiculous flamers on my rear at the start of his turn, but between the negative hit modifiers (for the fire prisms and wraith knight shooting and CC), drones, and invul saves, he wasn't able to completely destroy any of my teams. In my first turn, I was then able to drop my flamers with gun drones on one of the Wraith Guard teams and destroy it, 1st CIB team >9" from the second Wraith Guard team and destroy it, then drop 2x QFC within 8" of a knight to destroy it, and the second CIB team took the other knight down to 10 wounds with the help of shadowsun who luckily didn't have to move to be within 8".
To secure victory, the wise must adapt ~ Puretide