A little late to reply (5 years late.) but since I'm starting to play ME 2 I couldn't reply earlier.
I'm doing my first plathough as infiltrator on insanity playthough (I'm used to play games on this settings.), I already done the collector ship trap, currently doing loyality missions + recruiting.
I was just looking how things work, before really 'make a move' about optimal build.
The thing that I've noticed is, if you're not going for squad cryo, then level 1 is enough, since 3 seconds it good enough to instant killing the target or disabling it while you wipe out the remaining enemies.
Since I started thinking about how to make things better, I'll quickly comment about your three builds.
1 - This one seems pretty bad, honestly. My suggestion would be:
Disruptor Ammo: 4
Assassin's Cloak: 4
Heavy Incinerate: 4
AI Hacking: 1
Assassin: 4
Warp Ammo: 4
Assassin and cloak are the primary skills in here, disruptor is good against syntectics and shield, while warp covers armor, health and barrier, making you a perfect assassin in any circustance.
Incendiary because there's not other choice, at least the few seconds disable on organic enemies and some armor melting is pretty userful. AI hacking because there's one free point, so why not?
Also I would recommend the following squad members.
1 - Grunt or Jacobs, since a tanker which will suck damage is very important for this class. Jacobs is the second best tanker with biotics, and grunt is versatile between close and medium range, to not mention the best tanker.
2 - Legion or Kasumi or Garrus or Zaeed.
Build two: This one sounds really good actually, I personally would only change heavy cryo to squad, since it does trigger very often and the extra seconds are pointless. (better to do it more often with extra squad members and against more foes.)
However since this build CC mainly based on cryo ammo, I would suggest squad members with incineration or/and overload.
Also smg/assault rifles users are very valuable.
Build three: Sounds very good too, however it's cleary the hardest one to master, not only because it might needs a relocation of points and adaption, but mainly because it will be the hardest one to use properly and master what it can really do. So in sume, it will depends entirely on how well the player will absorb it's true potential adopting on a unique playstyle.
Also there's a need to adapt with squad members affinity as well.
So in short, build 2 and 3 sounds solid (3 being the hardest to master), build 1 however, does not.