In the default game, you can shoot an NPC while undetected and another NPC who is standing right beside the one you shot will not even react. With my mod, the second NPC with know right where you are (from your gun shot), and come after you.
So you consider the armored vault suit and leather armor (each being 15 lbs) to be heavy armor? Otherwise I agree with your evaluation of good sneaking practices and follow then religiously, but I still feel I get detected too easily when I'm unseen. I also agree that MOBs should be alerted by the gunshot (from non-silenced weapons), but at the same time I'm uneasy about the idea because when I don't get a sneak attack I can unload a full clip of 10mm into head and torso and still fail to take down simple raiders. By way of perspective, I'm at L6 with 62 sneak and 70 small guns, and I always keep my guns between ~2/3 and 3/4 repair.
My Survival module affects weapons and armor, but there is no easy answer to your critical head shot question, as there are just too many factors to consider.
Can you give me some examples of what factors you are referring to, beyond what I already mentioned about my character? Assume I'm using your Survival mod.
I was actually referring with how head crippling will affect MOBs. Like I said, it doesn't seem to have any effect in Vanilla.
For the most part I agree with regard to bullets, though I strongly disagree regarding melee, especially since I have 4 STR and only Grognak has done anything for my melee skill. Based on your experience though, do you think it would be possible (to extend sneak attack into caution mode)?
Edit: My game experience.
I loaded the full mod into a game in progress. The only other mods I was using originally were http://www.fallout3nexus.com/downloads/file.php?id=518, the Cross-Repair set (http://www.fallout3nexus.com/downloads/file.php?id=1838 and http://www.fallout3nexus.com/downloads/file.php?id=183) and some texture and music replacers. I'm L6 with 62 sneak and 65 SG (70 was with the Armored Vault Suit buff). My primary wep is the 10mm, which is reading 17 damage in it's current condition. Secondary is the hunting rifle which reads 44. On the path between the Minefield and the train station is where I did my testing; three Raiders patrol there. For me, two had SMGs and one had a knife or something. I tried my pistol first. Sneak attack crit to the head was at best around 1/3 HP. On average, it took a sneak crit plus 10 more shots, mostly torso, to take him down. When I managed mostly head shots it was 6-7 more rounds. Either way, by the time I accomplished this the other two were hot on me, and I got owned. So I tried the rifle. I took him out in one sneak crit, and I was barely able to escape at the slightly brisk walk which is my run speed. But I only tried that once, and I'd count it more as luck than anything else. Down to two now, I went for the one with the SMG. This one was about as tough as the first, taking between 5-11 more rounds after a crit sneak head shot. I was actually worse off when I went with the SMG the first raider dropped, which was quite a surprise considering how effective that weapon was against me. I did like how the guy with the knife went for the second guy's gun, but either way he was much weaker and went down in only 2-3 shots even without a sneak crit.
First, the good. There were a few times when I probably would have been detected in Vanilla, but wasn't with the mod. I was definitely made to take a more strategic path than I usually would (ie going for the gunners first), which is pleasing. And the melee raider grabbing the SMG on his way to attack me was fantastic. Good stuff indeed.
Now, the not so good. The penalty for wearing heavy armor is great in theory, but the cut-off is too low. I've not seen anything I would call armor below 10lbs; maybe the Tunnel Snake outfit, but it's a stretch to call that armor. And the penalty is definitely noticeable. I did a mere sidestep while wearing the Armored Vault Suit - I'm not even sure I actually moved position - and was detected at a much greater range than when I was when 'lightly' armored. Otherwise I wore a pre-war outfit.
I had mixed results with re-hiding, but generally one false move and any chance of surprise (or for that matter, survival) was out the window. And after being detected, forgeddaboudit. There's no running away since I can't, ya know, run. It's a stretch even to call it jogging. I remember how much trouble I had when I encountered the Talons at the metro. Essentially, I ran away and lost them. I can safely say that there is no way I would have survived that encounter with this mod enabled.
Moreover, the increased response of other MOBs generally ended as I suspected, ie. in a painful death (for me). It's definitely realistic, but I can't imagine actually playing through the game like this. The increased difficulty due to this aspect alone is not balanced out by any practical benefits that I can see. My pistol is still effectively obsolete even with well placed shots against raiders, which means so much for a silenced pistol regardless of how it might change the dynamic. I don't even want to imagine what it would take to kill a mutant. Not that I'd ever take on a mutant with a pistol, but if it scales I'm thinking at least the same number of rifle shots, all to the head. While on the subject of weapons, I hadn't paid any attention to Vanilla but the damage for a 10mm SMG (49 damage at ~40%) seems incredibly excessive when compared to the pistol, if it is damage per shot. If anything an SMG should do slightly less damage per shot than a pistol with the same ammo. If it is damage per second, though, maybe it makes sense. In any case, if it had been nearly as effective for me as it was against me I might have packed one for tight spots; but the severe decrease in carrying capacity (190 -> 70) means that carrying a wider variety of weapons (much less looting much of anything I come across) is out.
So there you have it, for what it's worth. The short of it being, this mod will not be remaining in my load order, at least not in its current state.